We sell an acer desktop, athlon X2 4400+ 2 gigs of ram, 320gig HD, dvd burner, vista premium for $399, and it runs the OS fine. Your dad that compaq (I'm familiar with it athlon 64, 512mb ram) because he was being cheap, at the time he could've bought an acer dual core with at least a gig of ram or another hp or compaq with a dual core cpu for like $50 more. Or he could've bought another gig of ram for like $10. Manufacturers have always sold under spec'd machines, emachines and compaq use to sell an XP machine with 128MB of ram.
I slapped XP on her and she was good as gold. No spontaneous BSOD 4 days later, no more 5 min bootup, no more 2 min to load a browser, no more 5-10 min to shut down.
I suppose I coulda even done Linux, but I figured I might use the computer to play a game when I have friends over or something haha