The basic 5boxing specs have been fairly standard among the scattered posts related to it that do pop up:

6600-series Intel Quad-Core Processors(AMD's just can't compete in performance, much as I <3 AMD)
8800 GT(not GTS) vidcard(get the 512mb ddr3 versions if possible; XFX brand ones usually have it)
4gb RAM is commonly accepted/necessary
Since you'd be switching from amd to intel you'd need a new mobo to go with it, differing sockets, which'll run around $100/50 pounds/euros/whatever it is that's worth twice as much as the dollar lol
If your PSU isn't at least 600, or 650w, I'd upgrade that too as 8800s + quadcores can eat a fair bit of power and with how big the 8800 is(long as mobo is, as tall as from mobo to case almost lol) you'll want decent air circulation too, a case fan at the least(My new case came with 2 + a meshed front; 1 up front pulling air into and through the HDs, and a 2nd in back blowing it out through a grate; my PSU has a huge fan on it's underside as well as the back blowing air through the case and out/away as well)
Feel like I'm forgetting something but I can't think of what...but either way if you shop around a lil you should be able to find all you need easily within your price range as I spent on all of the above + a few other items and it only ran me $900, which would be very much uneducated-guesstimated around 450 euro