Currently have XP3700+ 7900GT + 2GB DDR400
Your Videocard outperforms MOST new videocards such as Geforce8600GTS
It performs in between the 8800GTS and the 8600GTS so you should be pretty good for the next 8 months or so.
Your CPU is potentially as fast as it gets for a mobo using DDR400 Ram.
Because now everything runs on DDR2-667/800... DDR400 is more expensive. (not worth the upgrade since you already have 2gigs)
I would think you can run COD4 at high graphics with your rig...
I am a computer guy... not an artist... and I say get the guitar !!!
Your PC is still Pretty good for a while... unless of course you are a hard core gamer who needs something for Farcry2 / Crysis and whatever other crazy games come out.
Now I am VERY curious as of what CPU you have
AthlonXP's end at 3200
Then it goes to Athlon64 3000 to 3700 On the 754pin mobos (who got dropped real fast unfortunately)
Then Athlon64 3000 to 4600 I think on 939
Well those are for the ddr400 memory.