Just a thought that I think could potentially save you a lot of bucks. Don't buy that graphics card. No top of the range GFX card can actually run any Direct X 10 games at playable frame rates, so why buy any for Direct X 10 right now? Wait for the next gen.
Instead, by the best bang per buck Direct X 9 graphics card, which would be a ATI X1950XT 512MB for UKú110 which I guess with lack of UK tax be about US$160. It'll play ANY Direct X 9 game just as good as any other card within the speeds of the Direct X 10 cards also.
Forget about Direct X 10 card the now, they're currently no good at what they're ment to do - Direct X 10 games.
I'd also get a Core 2 Duo E4300, and overclock it to the bollocks. They easily clock and still run cool. Upp the FSB from 800MHz to 1333MHz. Also, the additional 2MB cache on the E6xxx series C2D do not benifit the CPU at all in benchmarks, and if it ever does, never by more than 5%. Mobo, I'd recomend my own, see my sig. Fully feature laden, with the only grip being the PCe lane running at 8x when used in SLI - something I'll never do, since your on a budget. Memory, i'd get 666MHz corsair value select to support the 1333MHz FSB.
OS, Vista Premium 64bit, see here for a settled argument (IMHO) -
Thats my 2P.