It would probably help to know the resolution of his monitor as well as the budget or generally following the advice in this thread, but something you can do straight away is change the CPU to i5 750 and hopefully put the savings from that into getting a 5850. If you are hoping to crossfire at some point you will need a power supply with four PCI-E power connectors, which is typically 750W units.
And Samsung Spinpoint F3 and Seagate Barracuda 7200.12 and Caviar Black at better performing drives at that capacity level.