I think the reason why he responded so grumpily is that MAME isn't about optimization or any of the things we want it for... it's to accurately emulate old hardware. Sure, we all get a great emulator that can play awesome old games, but the devs do it for a much different reason than why we WANT it.... if that makes any sense. Just check out the MAME faq and whatnot.
Anyway, as far as Pac-man roasting your machine, I'd check to see what settings you have for video and whatnot. Pac-man ran at what, 51 Hz? If you've got triple buffering or other sync options set, it might just be screwing things up.