Well it does get really gray on how you consider a "mainstream" OS. Windows 2000 was probably overall the best yet; it did everything an OS fundamentally needs to without the excess baggage of XP and I used it on home and business systems. Still do. If I wanted a nice reliable system that's limited to a 32 bit proc, I'd still go 2000 over XP. And it was pretty mainstreamed... especially after ME turned out to be released later and was far worse for the extra effort. There was a period where they "forgot" ME and 2000 came on everything.

I use XP x64. It's not "mainstream", but the compatibility modes should be largely similar to a 64 bit install of Vista. I have no problems at all. That might not change for a while for me either, not much about Vista makes me feel like I just gotta have it. But I go for simple, reliable, compatible, over aesthetics and gee whiz features. Anyway, I believe Vista uses the same WoW64 engine so it shouldn't be giving you troubles unless there is a conflict coming from elsewhere.

You might have a bad graphics card. 6200's are chosen from GPU's that have bad pipelines that get "locked out". Your card could be a very marginal version of the 6200 then. Also, low graphics ram could be a problem. The rest of your system should be ok.