If you are going to be using it for gaming you need a better vid card. It seems that Radeon is on top right now, about the best of those seems to be the 9800 series.
Now come the eternal question, amd or p4. Personally I would go with amd since you get a better bang for your buck. Also you can overclock it. If really want to go hardcore and overclock to extreme, it is best to watercool your chip. You'll need a psu that can handle whatever else you put in your comp. IE, if you want to put in multible hdd cdrom/rw, or dvd/rw, if you want the neon light effect. If you want to know more, I suggest browsning throught this site. there is a lot of great info on a lot of these post. Check it out, and good luck.
dfi nfII ultr infinity/asus p4s800
amd 2500xp m/p4 2.6
ati 9600/ati 9600 pro
512mb pc3200/512mb pc3200