Xbox can barely emulate N64 games. So anything before N64 the Xbox can emulate pretty well, anything after it cannot...
N64 games that are playable on the PC and other systems such as your Xbox are called roms. You run the roms (which are N64 game files) w/ an emulator (the emulator "emulates" the hardware in a N64).
rihgt682, man you are stepping into a whole new world if you never knew anything about roms and emulators! Get ready for a sweet sweet ride man! First, go to this site http://www.rom-world.com and download this Nintendo (NES) Emulator from the Emulator section, NESten v0.61. Then, after you have the emulator downloaded, download a rom for the nintendo in the roms section. Set up the emulator, and then open it up and click "file" then "load rom" Find the rom file you downloaded for the nintendo emulator and bam, your playin an NES game on your PC.