Dynasty Warriors 4 Cheats

Shu officers
Huang Zhong Clear Act IV of Shu.
Jiang Wei In Battle of Tian Shui Tales defeat all generals outside the castles. When Jiang Wei comes out, defeat his two subs, then lure him to Zhuge Liang.
Ma Chao In 'Battle of Cheng Du', defeat Ma Chao when he arrives as enemy reinforcements. After the battle, he will be unlocked.
Pang Tong Clear Act II of Shu.
Wei Yan Clear Act IV of Shu.
Yue Ying Clear Act IV of Shu
Zhao Yun Clear Act II of Shu.
Zhuge Liang Clear Act II of Shu.

Wei officers

Cao Ren Clear Chapter 3 in Wei musou mode.
Dian Wei Clear Chapter 1 in Wei musou mode.
Sima Yi Clear Chapter 4 in Wei musou mode.
Xu Chu Clear Chapter 2 in Wei musou mode.
Xu Huang Clear Chapter 1 in Wei musou mode.
Zhang He Clear 11 stages in Wei musou mode.
Zhang Liao Clear Battle of Xia Pi in Chapter 3 of Wei musou mode.
Zhen Ji Clear Chapter 3 in Wei musou mode.

Wu officers

Da Qiao During the 'Two Qiao's' Tales stage, locate and rescue both sisters (Da Qiao and Xiao Qiao) and escort them to the Escape Point.
Gan Ning In Battle of Xia Kou, defeat Gan Ning, after Act IV, he will be unlocked.
Lu Xun Clear Act IV of Wu.
Lü Meng Clear Act I of Wu.
Sun Ce Clear Act II of Wu.
Sun Quan Clear Act III of Wu.
Taishi Ci In 'Campaign for Wu Territory', defeat Taishi Ci. He will withdraw, and then rejoin the battle with Wu. He will be unlocked after this.
Xiao Qiao During the 'Two Qiao's' Tales stage, locate and rescue both sisters (Da Qiao and Xiao Qiao) and escort them to the Escape Point.
Zhou Tai Clear Act III of Wu.
Zhou Yu Clear Act II of Wu.

musalania officers

Dong Zhuo Complete Lü Bu's Musou mode once.
Lü Bu Complete any Kingdom's Musou mode once.
Yuan Shao Complete Wei's Musou mode once.

If you go as the Wu teem and bet the game and after that go back and beat the first few levels in this order

Yellow Turben fortress
Yellow Turben Rebelion

after that rather then going to the next set of levels that is after that it will take you to a hole new set of levels.
~cool huh~

Go to the level "Lu Bu's revult] And Defeat EVERY stupid stinking enamy even the ambush troops and then Lu Bu will get his level ten wepon.

Go to the Imperial Seal level [I posted how to get there in one of the hints below this one it is the first secret level you go to] And defeat every officer and troop [Or was it just officer] Anyway you might want to do both for two reasons.
#1: I'm not sure witch one it was.
#2: You are going to be waiting 30 minutes because the Imperial Seal wont appear untel there is only 1 minute left untel you lose and it will apear in the top left corner of the map if i remember right. If it is not there wherever it is when it appears the location of it will be pointed out on the map the second it comes in.

Red Hare Harness
Appearance: A red horse with decorative horsey clothes.
Effect: Fastest horse in the game
Commonly Used By: Lu Bu, Guan Yu
Side: LU BU
Item Found At: BATTLE OF XIA PI
How To Get: See Guan Yu meets Red Hare event(southeast peninsula). Cannot
kill any generals(including sub).
Valuable Item Location: Near Red Hare

How I Got It: I played on Normal and I was using Lu Bu. I played in my Musuo
mode with my little brother(Gan Ning). I ran towards the peninsula located
towards the south and waited for Guan Yu to show up. I saw him running at
me and I ran away form him(leaving him alone with Red Hare). Once I saw an
event where Guan Yu climbed onto the horse me and my brother double teamed
him and I finished him off. Seconds later an item box appeared near Red Hare
and I picked it up.
+Failures+
I experienced a point where Guan Yu did not go to red Hare, but instead went
to the east(right) side of the castle. I later discovered the reason for this.
My Zhang Liao killed Xu Zhu. I set the difficulty on Normal to prevent this.
If Guan Yu doesn't head toward Red Hare you should avoid him as well. The
first time you should see him is when he's running toward your Red Hare on
the peninsula.

Hex Mark Harness
Appearance: Dark grey horse with blue and white saddle
Effect: Unknown(checkout Q&A as to why this hasn't been updated)
Commonly Used By: Liu Bei
Scenario: YELLOW TURBAN(MUSUO MODE ONLY)
Item Found At: CAMPAIGN AGAINST LIU BEI
How To Get: You must first play the Yellow Turban Fort Defend Battle. Then
select the Liu Bei Invasion battle. Now, while playing Liu Bei Invasion you
should see Zhao Yun instead of Zhang Fei. Defeat Zhao Yun and Guan Yu before
the back-up troops appear. After that invade LIu Bei's castle and fight Liu
Bei until the Item Report appears. You'll either need to kill his surrounding
soldiers or lower his health a little bit.
Valuable Item Location: Left of the entry point in Cao Cao's castle.

How I got it: I had to use 2 players for this one. Me and my friend killed
both officers quickly. I wiped out Guan Yu real quick, while he dueled Zhao
Yun and killed him. After that Liu Bei tried to charge at us, and we eliminated
all his privates around him and the item report appeared.
+Failures+
Speed is the key here. If you kill Guan Yu or Zhao Yun and the message that
says you defeated them appears AFTER Huang Zhong appears you'll need to reset!
You MUST... 

When dealing with magical obstacles; i.e.: boulders, floods, wind
storms kill the magician that made it to deactivate the obstacle.
When it's military; i.e.: catapults, fire juggernauts, free-standing
forts. Destroy it with you're character attack.

This trick will take quite a long time, but is worth it. Before facing Lu Bu, charge up your Musou. Then, charge towards him (from behind, if possible). Use your Musou on him. After he is on the ground, use this chance to run away. Charge up your Musou again and return to attack him. Your Musou could be more powerful when your life bar is red. This will set Lu Bu on fire.
Take Lu Bu's Red Hare and run back and forth. Run him over and attack with Triangle to get weapon experience or just a normal Square attack. When he is almost dead, you can get off the horse and use Musou, or keep riding horse and lunge at him.
Use the following trick to defeat Lu Bu in a duel. When in Hu Lao Gate, Yuan Shao will say "Protect the ram while it heads for Hu Lao Gate". After the ram destroys Hu Lao's Gate, Yuan Shao will say "All forces march. Take Dong Zhuo's head." After that, Lu Bu will appear. A few seconds, later Lu Bu will say "You dare face the mighty Lu Bu" . Duel him. Use the following items as Zhao Yun on the easy difficulty settin to defeat him. Note: Also use Zhao Yun's Max combo, which is Square(2), Triangle(3). If done correctly, he should fly in the air, allowing you to land another combo. The items are: Tiger Amulet: 15, Tortoise Armulet: 19, Peacock Urn: 15, Dragon Armulet: 15, Wind Scroll: none. Make sure your character has almost maximum stats.
Use the following trick to defeat Lu Bu in a duel. This can be somewhat difficult to actually do, but if it works you can defeat Lu Bu in a duel easily. First, get your character's weapon to at least level 4. Going to all three of the Yellow Turban levels twice (and defeating most, if not all Generals and sub-Generals) should take care of this. Attack Lu Bu with the third charge (Square(2), Triangle) and keep pressing Triangle. You will notice that since the character has the second form of the weapon, they do more hits than before. When Lu Bu becomes dizzy from the last hit, get behind him and do a very strong combo (varies for each character). Keep doing this until he is defeated. Note: Some characters tend to push Lu Bu to the side, thus missing the blow that actually makes him dizzy (for example, Liu Bei, Sun Quan, Guan Yu, etc.). However, this does not make it impossible for them to pull this off.
To defeat Lu Bu in under ten minutes, when the battle of Hu Lao Gate starts, quickly get your gate open by defeating the General that blocks it (Li Ru, Dong Min, etc.). The battering ram should now... 

To get zhou tai's 10th weapon play the nanman campaign at free or musou mode(1 or 2 player)
under the hard difficulty.

First go and defeat king Mulu before Dong tu ne and Ahui nan defects.After that go inside the enemy main camp and you will receive your 10th weapon!

(Tip : a saddle makes it really easy)

Play The Battle Of Jian Ye level under the hard difficulty setting with Liu Bei's forces. You must play with Huang Zhong and defeat the officers with Huang Zhong. First, do not defeat any of the fake Sun Jians (that appear in four different places). Defeat Huang Gai, Taishi Ci, or Zhou Tai. This allows for the gates of the real Sun Jian's main camp to open. After this is done, you must defeat Sun Ce, Sun Quan, and Sun Shang Xiang at least once before any of them become commanders of the Wu army. A message stating that you have acquired Huang Zhong's level 10 weapon, the Oracle Sword, will appear. Then, finish the level.