My little bit of advice: I'm upgrading my current pc because I'm going into college myself this year and need a good pc for this (plus its a good summer project
I'm buying my new cpu, motherboard, RAM and graphics from the US! I did this before and got all the major (but not heavy!!) parts I've just listed from there and got someone I knew of to forward them over. Then I bought the optical and hard drives, plus the case, psu etc. locally as they wouldn't pay to send (heavy items!)
Saved me a fortune, maybe £100-150. If you can I'd say do that. The US has great prices!
Oh and the "Phenom II x4 940" seems your best bet if you can get it, however the "Phenom II x4 955" uses the AM3 socket and supports DDR3. Perhaps this would be better as DDR3 and the AM3 socket should be more future-proof than the DDR2 and AM2+ socket used by the 940, i.e. You could swap out the processor in 2-3 years time?
Sadly the 955 is a tad bit overpriced at the moment I think