Everything above kilo (1,000) is expressed with a capital letter so Mb and Gb; mb is millibytes (one thousandth of a byte) - Guardian correction
Called NESCafe, the emulator works through Media Center on the Xbox 360 and it does have limitations. The inventor who goes by the handle "Xexter" has not found a way to add a menu for the roms list so you will have to edit the nes.htm and change to whatever Nes rom you want to play.
This "Xexter" has included a Public Domain rom for testing but claims to have got Zelda1-2, Excitebike, and TecmoBowl working. He says you can find the Roms for these online.