For development and QA, virtual servers work great. Here are the specs of one I put together that is running a virtual database server, web server, three XP systems, one Vista system, and I even threw on Win95 and yes, DOS 6.22 with Windows For Workgroups 3.11 just for the hell of it!

ABIT Fatal1ty F-I90HD Micro ATX Intel Motherboard $106.99

Seagate Barracuda 7200.10 250GB 3.5" SATA 3.0Gb/s Hard Drive $69.99

Intel Core 2 Duo E6550 2.33GHz LGA 775 Processor $174.99

SAMSUNG 20X DVD±R DVD Burner Black SATA Model SH-S203B $29.99

Foxconn TLM041-CN300C-01 Black Computer Case $34.99

G.SKILL 8GB 240-Pin DDR2 SDRAM DDR2 667 (PC2 5300) $299.98

Grand Total: $716.93

We have since added a second hard drive and do have the capability of RAID.

I just run Microsoft Virtual Server 2005, which is free and works great for my needs.