Finally, a good answer :) thank you.
* While I was using Vista, it took about ~800-900mb of ram, with everything that I need installed. I have 2 gigs. Also, i fount one nice thing. Vista adopts to your amount of ram. If you have less, it will take less. :)
Now I am using XP (for testing purposes). And it takes ~600mb of ram. The difference is ~300mb. Not so much, if you have 2 or 4GB of ram :)
* As I know, now all drivers go for xp and vista. All drivers that I need, I can find it for vista and xp. Event my old PC's (3-4 years old) hardware has drivers for vista. Conclusion: I think that driver problem were there only when vista has started. If I am wrong, please, correct me. :)
* Problems with soft... Hm... I dunno, everything works greatly for me... Sometimes you need to let the program run in administrator mode, that could fix the problem? I really dunno, because like I said, totally everything that I've tried on Vista worked great! :/
* Vista has DX10! If your GPU is new and can handle DX10, go for Vista. On XP its 9.0c. Whats new on dx10? You can read a small article: http://www.extremetech.com/article2/0,1697,1931918,00.asp
That's it for now =)