Yeah similar thing happened to me from buying from PC -Specialist. The PC just doesn't perform how I'd hoped and now seriously considering buying a new faster more reliable machine. Trouble is most of the retailers seem to have some unsatisfied customers so it is hard to choose. One firm on here getting a lot of good feedback is Cougar click here
I'm thinking of buying from them just trying to decide on how I should have my hard drives set up as I want to use the machine for photoshop C3 and other graphic software.
The spec you listed sounds good to me, I have a 7600GT card in this machine and it is certainly adequate for my games use. Still though I've not seen one of these new cards like the Nvidia GeForce 8800GTX 768mb so don't know how much better they are.