Now if you want a 'real' computer and spend a few bucks, 6000 or so, we can hook you up!
Just make sure you do not move it too much as it is not a lightweight.
It will hold up to 32 GB ram and runs Server 2008 as the host and you can run multiple virtualized OS guests.
Run XP Pro and play with other versions.
It can pull up to 10 amps when loaded.http://www.supermicro.com/products/chassis/4U/745/SC745TQ-R800.cfm
2 x XEON Quad Harpertown E5410 2.3
4 x 2G DDR2 PC2-4200 ECC
800W redundant power supply
Adaptec 3805 SATA RAID
2 X 320G 16M RE3 WD SATA RAID1 C: OS Hypervision
2 X 320G 16M RE3 WD SATA RAID1 D: Guest
2 X 320G 16M RE3 WD SATA RAID1 E: SQL
1 X 320G 16M RE3 WD SATA hot spare
1 - 1T WD RE3 snapshots
A good custom built computer with quality name brand parts built by a reputable local company is your best bet.
Expect to pay about $1100 at your local shop and you will not be disapointed.
Spend $500 at the big box store every 3 years.