Well Sleong it sounds like you shouldn't have an issue using Windows. Most of everyone's posts I have read on here have taken to Windows XP. It's cheaper to buy, strong enough to run any MAME, and it's not as 'full' as 7. I can't speak for anything but Maximus Arcade. I have used it and if you follow tabs its really not that hard to configure. There are many tutorials. I have also heard that hyperspin is excellent to work with. The originator of the weecade has updated his website with a plethora of ways to go as far as Operating Systems and Front Ends go. It can be found
here. Like everyone states it's not smart to talk about Emulators. (I feel like emulators have turned into Voldemort. "They which should not be named!"

) Anyway. Just do a Google search for emulator ratings and you should come up with some valuable information. Most websites that do carry Roms and Emulators usually have a rating software like any other program.
As for hardware I agree with PaigeOliver but don't get a system that is really old. Fun Fact: Tried to use my system from 2000 to start a Fix It Felix Cab for my nieces. P3 1GB of memory. It wasnt happy. Did it run XP? Yes. But the version of Sjaaks FIF requires the version of dot net framework 4.0 that wouldn't run. I got to 3.5. Needless to say I went on a quick search and found a system considerably cheap that would run it. Its being shipped this week. The basic outline for the system is as follows: Dell Refurbished Black 745 Desktop PC with Intel Core 2 Duo Processor, 2GB Memory, 80GB Hard Drive and Windows 7 Home Premium (Monitor Not Included).
I too have a Athlon 64 system that I run my weecade on. I have SF2 installed and it runs fine. I'll get you my specs for my weecade when I get home. Otherwise if you use Ubuntu (it sounds like you know a little something about computers)
here are PS3's specs. Just go off of these to gauge what your computer will run if you are going to go as far as emulating PS3 games. Just a word to the wise. I played Sonic on my weecade the other day and if felt weird not having a controller. You could also do what some have done and add a USB wired or wireless game pad and use that when you want to get the feel of the home console. I have a feeling I will do this in the future. I have a spare Microsoft Windows XBOX 360 controller laying around. Plus its kind of a nuisance trying to play and the emulator pulls up a window because the emulator interprets the arcade control as keyboard shortcuts. Learned that the hard way by also playing Sonic.
Anyway. I'm done. Go play. Don't be afraid to experiment and ask questions. Good luck.