I'm currently using XP SP1 & mameWAH on my cabinet
supporting these fine systems:
Mame, vpinball, PSX, atari2600, atari5200, atari7800, atari jaguar, atari lynx, gamegear, GB, GBC, GBA, Dreamcast, Amiga, C64, Snes, Nes, N64, genesis, SMS, sega32X, msx1, msx2, AppleII, Colecovision & Odyssey2 (mostly using MESS for the emulation)
(total of +- 150000 roms)

Some PC games (Battlefield, Wolfenstein, Actua soccer, Syndicate, Doom, Monopoly, etc..)
SK-jukebox with +- 1500 albums
VLC media viewer for all the Simpsons seasons & many other cartoons
Daemon Tools for virtual CD
TV card & recorder with remote control
Optical Keyboard & Mouse
Total installed HD space = 760 GB (4HDs & No CD-ROM)