I still have a 2003 build in my closet that I use every so often to ftp stuff to my xbox lan.
AMD Barton 2500
Windows XP
Some Leadtek video card
1 gig of ram.
250gig HD
My second oldest is a 2007 build that I use still for mainly data storage:
Intel Core2Duo 3.0Ghz
2 gigs of DDR2
Windows XP
Geforce 8600
An old Enlight case I still have with a Pentium III 733mhz in it...don't use it anymore. Thought about putting a modern setup in there, low power of course.