Rosewill Black ATX Mid Tower Case, Model "R214P" $29.50
Lite-On Black 52X32X52X16 Combo Drive, Model SOHC-5232K, OEM Bulk Pack $36.99
SAMSUNG 80GB 7200RPM IDE Hard Drive, Model SP0802N, OEM Drive only $56.50
ASUS "A7N8X" nForce2 Ultra 400 Chipset Motherboard for AMD Socket A CPU -RETAIL(New Version, now support AMD Barton 400MHz) $72.00
SAPPHIRE ATI RADEON 9600SE Video Card, 128MB DDR, 64-bit, DVI/TV-Out, 8X AGP, Model "ATLANTIS RADEON 9600SE" -RETAIL $71.70
PDP SYSTEMS Memory Dual Channel Kit 184-Pin 512MB (256MBx2) DDR PC-2700, Model PDC5122700LLK - Retail $83.00
AMD Athlon XP 2700+, 333MHz FSB, 256K Cache Processor - Retail $103.00
Total (without shipping and tax) $415.50 from Newegg.com
Your spare $84.50 could upgrade you to a 200GB drive and get you a DVD burner. But I thought I'd leave it cheap just to prove you can play HL2 for this price.