Zapdos can be found outside of the power plant in Kanto after you recover a stolen part from the power plant which was hidden in the Cerulian gym on the life preservers next to the water. After you bring it back to the power plant and return it fly to a different place then go back to the power plant and Zapdoz is is waiting on the side, ( is level 50 ).
Moltres is somewhere towards the top of mt Silver which you can get to by beating all Kanto gyms and entering through the left path that has a guard by it.
Articuno is on seafoam islands.
After chasing Suicune around for a while and you get to the route with the wind mills you will get to battle and try to catch Suicune on the Cerulian cope after you find Misty with a guy up there.
Latios apears after you take to some guy in Kanto that says a rare blue pokemon from Hoenn has been appearing. On your map you will see a Latios icon that you chase to catch.
Same with Raikou and Entei, you can start chasing them around after you find them in the burned tower.
Lugia is in the upper right island of the Whirl Islandsbut you should save every so often so you dont mess up but it will only appear if you have the items: Silver Wing (get from radio manager after defeating team rocket and rescuing him)and Tidal Bell (kommono girls give it to you), and have beaten all five Komono girls and they ask you to meet them there. Opposite with Heart Gold version you need a Rainbow Wing insted of a Silver Wing but the same other necessites, besides the fact Ho-oh is at the top of the Bell Tower.
Whats really cool is that you can catch both in both games. Theres a man in Pewter city on a raised piece of ground that gives the other one (Silver or Rainbow) and you just go to the other one.
Latias I don't know.......
Finally Lapras is in the Union cave off route 33 (only on Fridays)once you enter it if you go up and to the right water is on both sides of you go to the water below you and follow the stairs to the next room with two Poke'matics and go down those stairs. Now you should be in a big room, follow the water down, tothe left, down again, untill you hit land. Now you follow until at bottom of the screen, battle the one trainer, then surf to the middle of the pond to the right, talk to Lapras (level 20)and catch it. Tip: save before talking to it so you can turn your game off and back on and sometimes the gender changes.