I would suggest trying a live CD of a linux distro (ie Fedora, Ubuntu, SuSE, etc) but I don't think that its possible to do that on a PS3. Right now, I'm actualy on my desktop which is running Ubuntu. On my laptop I have it dual booted with Vista and Ubuntu (reminds me, I need to work on getting my internal wireless card to work with ubuntu on there, but thats besides the point).
As for Mac, last time I used one was my partners MacBook back in June. In terms of start up, both are fast (hell, ironically, MacBooks dual booted with Vista boot up, load, and run faster than an actual PC one).
Compatability wise, with linux, you'll have to download the codecs more so than with windows. For example, to play an mp3 (which is in Windows now), you have to download the codec. The only problem I have had is avi files. But I've fixed that mostly (ironically, the avi files that Vista won't play, I have no problems with on linux).
If you want open source, linux FTW all the way! If any fellow CAGs are MacHeads, please chime in about Mac and open source lol. Though, if you want, next time I talk to my partner I can ask him as well.
Now I do have a question, do you currently own a PS3? If not, by the time you get a mini Mac or a PS3 and feel like getting really froggy putting linux on it, you might as well buy a laptop. Either a decent Vista one (ie at least 2 gigs of RAM, big hard drive, good video card, and such) or a MacBook (which would be the more expensive route). I'm suggesting laptop since you said you'll be using it for school work (if your in college, then I would definatly go with a laptop). Of those two, you can have both the original OS and linux. Though Dell offers laptops and desktops with Ubuntu installed.
And if you're only interested in PS1 and PS2 games, best option would be to go with either a PC or Mac and a PS2.
Hope I wasn't getting too techy or anything, if theres anything you need help with, I'll try my best