Yes, me again with a cheat for the 100m Freestyle. It's not really a cheat its just all
the characters in the game and which move with the stylus you have to use. Starting with:

LEFT TO RIGHT (running technique) (doggy-paddle)
Yoshi the Dinosaur
Sonic the Hedgheog
Miles "Tails" Prower the Fox

UP TO DOWN (turn the DS on its side, and do same technique for running) (frontstroke)
Shadow the Hedgehog (my fave character)
Luigi
Mario
Princess Daisy
Princess Peach

SMILEY FACE (KIND OF) (the smile bit for to complete a face, rub to one side then to the
other) (butterfly)
Knuckles the Echidna
Waluigi
Blaze the Cat

CIRCLE (same technique as hammer throw) (breast stroke)
Amy-Rose the Hedgehog
Bowser
Dr. Eggman
Wario

FIGURE OF EIGHT (side to side, like a dolphin/seal) (dunno the name for it :$)
Vector the Alligator

I hope this helps you decide. If you want a tip from me, use the one with the Hammer Throw
technique if you are a Pro at the Hammer Throw (like me). But, if you are a Running master
(kind of like me), use the left to right techniques. But if you don't want to remember
loads, choose these characters:
Tails
Sonic
Yoshi
Amy-Rose
Bowser
Dr. Eggman
Wario

hope i helped! (again) oh yes, have a nice day =D