If you can then build your own. Then you can have exactly what you want in your PC. Look at Zingles guide and it will explain all you need to know. It may work out that you get more for your money
At your budget you should be able to afford a Core 2 Duo machine
Or if your willing to go a little bit over you could have a Core 2 Quad machine
If you dont want to build your own this is good except for the gfx
http://www.ebuyer.com/product/128464
Its also out of stock tho