450W PSU: $60
Intel E6420: $220 ($180 for E6320)
ASRock Dual-775Vista: ~$75
2x1GB Corsair DDR2: ~$85
Video card: $130 (the mobo listed takes AGP or PCIe, I have it on my PC)
SATA HD, 160GB or so: ~$150
Soundcard: onboard sound ($0)
Depends no if you need all the "extras" -- CDROMs, keyboards, speakers, etc... For this "baseline" of parts, you only spend $720 ($680 if you go with E6320). If you already have a vid card, shave off $130 (it'll take what you've got). If you already have a SATA HD, shave off another $150. If you already have DDR2 (mobo also takes DDR1, 2 slots each type, 2 GB max each type, only one type at a time) shave off another $85.
So, if you are "upgrading" and have RAM, Vid card, HD, etc, just the essentials come to:
450W PSU: $60
Intel E6420: $220 ($180 for E6320)
ASRock Dual-775Vista: ~$75
That's $355 ($315 for E6320)
I'd avoid the Intel E4000 series of chips, personally.