Motherboard: ASUS M3A
Processor: AMD Athlon 64 X2 3600+ 2.0 GHz (Windsor)
Graphics: ATi Radeon HD 3450 w/ 256 MB GDDR2 VRAM
Power Supply: 500W
Cooling: AMD Stock
Memory: 2GB Kingston DDR2-667 RAM
Hard Drive: Western Digital Caviar Blue 500 GB 7200 RPM w/ 16 MB Cache
Optical Drive: LG DVD-RW (IDE)
Operating System: Windows Vista Home Premium x64 SP1
TV Tuner: ATi TV Wonder 650 Combo USB
It cost me $560 (tax. incl.) but O/S price not incl.
Canada Computers has a system for $300, so add a tuner, vid card and an extra HDD would put you at the $400 margin then add tax and OS would be about $520.