Well as far as XP goes, very stable, very good with AMD since the support for the AMD is better under XP then many other OS´s.
Win ME.. now thats a big virus!
BG2 runs beatiful under WinXP, just get the XP patch and you are set to go. I have so far been able to run all the interesting games I want under winxp, I don´t play and DOS games though...
NTFS Is really great, tells you when something is weird and then fix it. What you need to do is to explore the new system since it is different from the Win98 settings. Also get a good feel for it, and turn off all thoose blimey eye-catching-graphic things.
Blääärgh, shades, and opacity and other processor stealing things.. :S