No. because wii is by Nintendo and Xbox is by Microsoft. That's why gamecube games play on the wii, they are both by Nintendo. Like how you can play gameboy games on the DS they are both Nintendo handhelds.
Probably not, (Ahem) There are 2 regions of Wiis. PAL and NTSC. PAL Wiis can only play PAL games. NTSC games can only be played by NTSC Wiis. NTSC is usually for The USA, PAL is generally for everywhere else. There are also NTSC-J Wiis in japan.