Gaming rig guide £400-£500

Ok I'm from the UK, My budget is £400-£500 My aim is to run Microsoft flight simulator x decently, I need everything ect, mouse keyboard, The only thing I don't need is the monitor, speakers and flight simulator x if you could direct me to some links or give me advice it would be greatly appreciated , thanks.

Look at this article from Bit-Tech:
What Hardware Should I Buy? - October 2009 / Affordable All Rounder

They explain why they recommend the Athlon II X2 250 Regor 3.0GHz CPU and Socket AM3 motherboard.
If you're interested in overclocking you can get the Phenom X2 550 Black Edition CPU for £20 more.

The E7500 is a bit more powerful CPU but the GTS 250 (9800GTX) is a good step up from the 9600GT.
All in all it should be very little difference in FSX performance while giving you better future upgrade options.

If you do decide to go with the E7500 (check the prices on E7400s too) I'd suggest a Gigabyte GA-EP43-DS3L.
You can go through back issues of 'What Hardware Should I Buy?' to see how recommendations have changed over time. They're linked at the bottom of the page.