Built a system out of old parts from the parts bin...
Celeron 2.4 socket 478
40GB hard drive
512mb (2x256 pc133) ram (has 2 slots for ddr ram as well)
PCI network card
56k modem
32mb AGP video card
P4VMM2 motherboard w/built in sound, nic and video
Generic 300w power supply
52x CD Writer
ASUS case
Legit copy of Windows XP Pro SP3
no keyboard or mouse
$100
w/17" LCD - add $50
w/DVD writer instead of CD writer - add $15
w/FX5500 128mb video card instead of 32mb - add $15