Sheesh there's been a lot of negativity and sarcasm on these forums for awhile now.

It's why I hardly ever post anymore.
Yeah, I get that the guy posted his CP, people (rightfully so) pointed out what was wrong with it, and he freaked out a little. But, I think that's a pretty natural reaction after spending so much money on the thing, the guy apologized, fixed the issues, thanked us more than once, and even invited us over to come play on it. And truthfully, I think his setup looks awesome. I'm over 1000 miles away, but if I were close, I'd have been one of the first ones to take him up on coming over and playing some games.

But you guys are gonna be rude and sarcastic to someone who asks for help because...you don't like his CP or whatever? Oh gimmie a break.

Anyway, to the subject at hand:
Mario Kart 64 looks so sweet on MAME
Mario Kart 64 does not run in Mame. You can read up on Mame here:
http://en.wikipedia.org/wiki/MAME and emulators in general here:
http://en.wikipedia.org/wiki/Emulator, but the gist of it is that Mame is an acronym that stands for Multiple Arcade Machine Emulator. It is software that mimics the inner workings of several types of arcade hardware, thus it does not run Mario Kart 64, which ran on the Nintendo 64. For that you would need a Nintendo 64 emulator.
As for your speed issue, if it was happening no matter what mode you're playing in, you would probably need to look for a throttle setting in your Nintendo 64 emulator and turn it on. But if it's only happening in 4 player games of Mario Kart 64 as you seem to be indicating, then it's either an emulation bug or an issue with a plugin. You might be able to fix that by using a different emulator or a different plugin for your current emulator, but setting that stuff up and getting it to play nice with a front end can be difficult even for those with experience. I think your best bet is to try the European rom fix that was suggested to you, and if that works, call it a day.

Hope this answers your question.