Item numbers and pricing direct from Newegg.com
Motherboard
GIGABYTE GA-P35-DS3L LGA 775 Intel P35 ATX All Solid Capacitor Intel Motherboard
89.99
Processor
Intel Core 2 Duo E8400 Wolfdale 3.0GHz 6MB L2 Cache LGA 775 65W Dual-Core Processor
$239.99
Ram
G.SKILL 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model F2-6400CL5D-2GBNQ
$44.99
Video Card
MSI NX8400GS-TD256EH GeForce 8400GS 256MB 64-bit GDDR2 PCI Express x16 Video Card
$37.99
Power supply
COOLER MASTER eXtreme Power RP-550-PCAR ATX from factor 12V V2.01 550W Power Supply
$59.99
Cpu Cooler A must for any custom machine, seriously why not?
ZALMAN CNPS9500 AT 2 Ball CPU Cooling Fan/Heatsink
42.99
Hard Drive
Seagate Barracuda 7200.10 ST3320820A 320GB 7200 RPM IDE Ultra ATA100 Hard Drive - OEM
74.99
And all for a grand total of ..................... $590.93 + shipping
Not a bad spec, but I'd change a couple of things:
First the Zalman Fans are way over-rated, everyone uses them in their review because they look great and are quite, the best value for money heatsink out the currently in my mind is the Cooler Master Hyper 212, Newegg don't stock it so you have to shop around a bit but they are cheaper than the Zalman and offer better cooling, and a bit of tape down the side of the fins to act as a duct will only improve the cooling preformance.
The graphics card, grab a gigabyte 2400pro, a little more but more reliable with all soid capacitors like their preformance motherboards.
Hard Drive, SATA all the way, IDE is dead just no one told it yet. Stick with Western Digital there are alot more reliable and quiter. Trust me on this one I work for a company that sells 10,000s of hard drives a month, most seagate & western digital, the WD failure rate is a lot lower than any other brand.
The last one to watch out for is the RAM speed, The G.Skill tends to overclock well, but if you want to make life easy for yourself get DDR2-1066 RAM, this way you can easily overclock to 4.0ghz without the need to complicate thinks by having to overclock you ram too, DDR2-800 will only get you to 3.6ghz with a E8400 before you need to overclock the RAM also. You can pick up corsair TWIN2X2048-8500C5 for only a little more than the G.Skill as long as you grab it with a rebate, $10 more will normally get you the Dominator DHX version of the same ram.