Nope, the Wii is not cross-platform compatible. Likewise, the PS3 doesn't play Wii games, the XBox360 doesn't play PS3 games, etc.
yes
super smash bros ,077 quantum of solas , call of duty 4 and 5, guitar hero all the games that have a little blue wifi symbol in the top right corner. :)
No, they can't.
no