I agree with brainy on this, go with a single core AMD 3200 would be my pick,
that way you could drop a little extra on the video card, a single 7800gt is a very good pick but in this case I would go for the XFX 6800gs xtreame which is a damn good card for little price. Just to give you a few ideas here but do the research first before you drop the bones.
things I wouldn't skimp on are the PSU, memory, case ( good air flow ), mobo
good brands are: PC power and cooling, OCZ, Antec, enermax, seasonic, fortron source for PSU!
Try if you can to set yourself up with good stuff that is upgradeable that way when you want too you can with little investment down the road.
good luck