I will take the other 39 cents than
You got yourself a nice PC now, you can easily throw in the newest and latest graphics card, for now and the future (7800GTX / ATI X900XTPE). But your current card handles those games with ease.
You can throw in a dual core 4800+ into that motherboard if you want to in the future, and even faster CPU's.
If you want to run two graphics card's, you can do the SLI mod to the motherboard and it will work (Slightly risky)
When you learn a bit more, and get a better heatsink and fan, you can overclock the crap outta that PC as well.
What did you do for the case and the hard drive, and what of the two card's did you choose?