I am sorry to have to correct you, eurasian, but having a power supply that is too powerful should not be an issue, unless it's a crappy power supply. It should deliver exactly the amount of power necessary. That being said, the system he is building only needs a 350 watt power supply, but I'd recommend 500 watt if he's thinking of getting a 8800 GTS, or a 450 watt for a power supply like I have: the 7950GT.
Krimy:
It was fun reading this thread, and there is plenty of good information and misinformation floating around here. Most of what you have been told is correct, and you should be fine with your choice.
I would like to chime in however:
Yes, I agree with eurasian, get the Seagate Barracuda 7200.10 16MB Cache 320 GB hard drive. (or 250)
Get a 500 watt power supply from a reputable company. Seasonic is an excellent choice, but expensive. I got an Enermax Noisetaker, but there's nothing special about it except the efficiency (and they make good power supplies, of course)
You going to wait for a 8800GTS to come down in price? Please. The DX10 games aren't going to be out for a while, and even when they do, they will play perfectly well on a DX9 card, especially if you like to run them at 1024x768. Furthermore, you will need Windows Vista for DX10; do you plan on getting Vista? I recently got the 7950GT, but the radeon 1950XT is probably a better buy now.
Get a sound card. The asus boards are very good, but known to have crappy sound and crackling. The Audigy 4 SE that I got from Newegg will be good for you, as it offloads the processing from the cpu to the sound card, and sounds good. You can get an x-fi if you have high fidelity ears, and like to burn money!
I chose the Asus P5B-E, which is in between the P5B and P5B deluxe. It has firewire and overclockability, but not as good overclockability as the deluxe. However, as you are not planning to overclock, unless you want a firewire port, the P5B will be an adequate, stable board for you.
Get the Corsair 800 XMS2 ram. I recommend strongly against OCZ: They have compatibility issues, and sometimes, stability issues. I am running the corsair 667, and I can guarantee that will work.
If you don't mind doing a little extra work when you put the build together, get arctic silver 5 paste. Instructions on how to apply are at arcticsilver.com
Nice case
Bruce