@Gorath - I am on very limited budget so cheaper CPU would be preferable but it is supposed to be a gaming machine so are you positive that ADM CPU will not affect performance of current and near future games like LA Noire, Skyrim, Mass Effect 3 or Dishonored? I am not greedy, I don't need to be able to play them on highest settings but I want something better than lowest settings! And yes, I am aware about the importance of graphic card
I'll give you a couple of links to brand new (some are from this week) Gamestar Mag articles. Sorry that they're in German, but they are exactly what you need. You can translate paragraphs or the whole page with
Babel Fish.
Their current recommendations for self built PCs. They claim their
500 EUR AMD Phenom 2 X4 PC is fast enough to play Crysis 2 at FullHD 1080p with high details. This PC is very similar to what I have, with the exception of my slower graphics card. I played Crysis 2 at 1680*1050, so FullHD with a faster card sounds realistic.
The
1000 EUR Intel i5 2500 PC is on the next page. It's full of luxury items though. After reading the article again, I believe the price difference isn't much bigger than 100 EUR if you choose identical components as far as possible. So mixing both configurations up is also very tempting. Especially the graphics card looks intersting.
100 EUR difference is less than I expected. That's a free graphics card upgrade as per the configurations above. I think all 4 options (more / less CPU resp. graphics card) are completely valid and attractive.
The latest Gamestar
CPU recommendations for gaming:
1. < 150 EUR:
budget: AMD Phenom II X4 960T (105 EUR) | Performance-tip: AMD FX 6100 (125 EUR)
2. 150 EUR < x < 250 EUR
Preis-Tip: Intel Core i5 2500(K*) (185 EUR) | Performance-Tip: Intel Core i7 2600 (250 EUR + 20 EUR K*)
*K -> can easily be overclocked.
So lots of options - and all are much faster than your current PC.
edit:
I see you have a nice sound card. Maybe you can find a mainboard with enough slots to continue to use it. Graphics cards with silent coolers are big.
As Pladio mentioned, an upgrade to Win7 is inevitable.