I'd start with a Shuttle case and go from there. Every base Shuttle will fit all of the above, with the P series chassis offering space for 4 total hard drives.

As far a s a great gaming card, it all depends on how much you want to spend for one. $200 range, I'm still sold on the peformance you get from an NVidia 6600 GT. $300-$400, start looking at the ATI X800 lineup. More then that, you might find an X850 XT PE (joke around the net is the PE stands for Phantom Edition, but it should be easier to find now that the card has been out for a few months).

CPU wise, I'd advise an Athlon 64 socket 939 of some speed. Again all depends on your price range. Dual core at a reasonable price still seems to be many months, if not a year off for the PC world.