Haven't played Half Life 2 have you? LOL, it is a major ram hog. The more ram with that game, the better. I have 1GB right now, and it still moves to virtual memory to play smoothly.
The powersupply is plenty adequate for a 3400+ you guys. He doesn't have like 4 Hardrives or an x800pro/6800GT or anything either. The 5700 is a great card, I loved my old one. It was very overclockable, and didn't produce a lot of heat for how far I had it overclocked.
Overall, I give that system a 9.4 outta 10. The powersupply could maybe use an upgrade (although unessecary) and it should really have 1GB or 768MB ram. 3X256MB DDR1 chips scream! Try that config. The more you have the total ram seperated, the faster the PC.
EX- 1X1GB chip= fast
2X512MB chips= faster
4X256MB chips= screaming!
That is simply because the Ram can do more multitasking because all the data doesn't have to pile into one chip and come out of one chip, but rather go into 2 or 4 chips, and come back out of more chips. This is always a good idea when doing ram configs.