mysetup:
AMD 3700 1MB Cache
1x 320GB HD (8mb cache)
1x 6800GS Nvidia GPU
1x 1GB PC3200
1x Asus MB - can't remember model number
1x AL1914 (acer 19" lcd)
I can't say enough for having a case with 4 or more case fans in it, mine are so soft I can't hardly hear them!
I play any game I have (battle field 2, sims 2, tiger woods 2k5 and 2k6, 7 sins, black and white 2) in max details on everything and @ 1024x768 with no hicups on the video card. I'd say go with something a lil more high end like the 7600 or 7900 version, but the 7300 is a damn nice card itself and wont give you no problems.
go with AMD and a Asus/Abit combination, you might want dual core, if you do, then do it right and go AMD, read the reviews intel can't seem to do it right or as good as AMD and there X2 line of chips. Dual core AMD I say 3800X2 or 4000X2. Single core, I still say AMD 3700 w/ 1MB cache (the come with 512 also, get the 1mb version of ANY single core chip if available!)
Most games require 1GB of ram now to run "correctly", I say go with 2GB for now and make sure you leave room for the 4GB later, you wont need it now and you wont need it for vista right away, however you will need it eventually....maybe....
I'm not an Intel fan, i'm just a fan of what I know and what I know works for me. I run my own small business and am an avid gamer, my business PC and game rig sit side by side and both are AMD custom built by me.
BTW dont cheap out on the case, but dont get water cooling or those stupid "phase change" cases either, there stupid and useless! you WILL need 4 or more fans, but have no fear they are NOT loud, my older rig w/ 2 fans is louder than my rig with 4 fans, and the 2 fan unit is further away!
all in all save where you can and splurg on the following:
SATA II Hard Drives with atleast 8 - 16mb cache
Video Cards (7300 -> Higher, ATLEAST 256MB Ram on the cards)
DDR PC3200 for the AMD chips
dont forget the floppy drive!