If I have animal crossing wild world and my friend has animal crossing: city folk, can he move in 2 my town?

Question

Don't say "I Don't Know" because I know no north americans have the game yet.

Answer 1

Nope. His code won't work with yours. But you can move into his town.  

His newer code acn absorb your older. But because yours is older, It can't handle new changes.

Sort of like how a DS can play a GBA game, but a GBA can't play a DS game.

Answer 2

No, because what if the character is wearing a shirt that's in AC:CF but not in AC:WW? You can however, transfer a Wild World character to AC:CF using the "DS Suitcase" feature, and that character's catalog will be transfered.