Everything was the same. I was using the same version of the CCCP codec pack, which always includes the lasted xVid. Same XP Pro with the same SPs and updates, same admin rights, etc. As far as video-playing apps: WMP, Media Player Classic, and Nero are on both machines. I actually ran Mala/MAME from a WD portable lappy drive on both machines. The only real difference was hardware, and since I don't really suspect hyperthreading, I assumed it was the video. The Quadro's are nice for solid modeling and all, but kinda weird with game-type-stuff. I'm also using the nVidia software on the Quadro, and I let windows handle the settings on the 8800.
Since I don't play MAME at work, I just gave it a quick "eh, I'ts not playing right" and moved on. And because it is at work, I can't really spend half a day playing with drivers and codecs and such. At least not lately.

BTW, these are with Circo's HQ vids.