I've managed to survived on a P4 2ghx machine, with 768 megs of RAM and a GeForce 3 with 64megs of memory :-) But then I tend to buy a new machine every three or four years and then buy a new one when its past its sell by date.
Still, now that I have a RL business that earns bits of its revenue from
EU/SL and other RCE based games decided to buy a computer through it. So gone for a quad core, with 4gbs RAM, 8800 GT card on a SLI motherboard. Cost about £1000 and should be a good step up for next years gaming.