Hi there! I still have a Pentium 3 @ 1.4GHz. Its got a Radeon in the upper 9x series card in it, and can run 720p media perfectly, Windows XP with K-lite codec pack, Winamp etc.. I still use Winamp anyway on my i5 as it's still brilliant. Mainly, it can support a disk drive, which I need to make a system disk for a Midi sequencer :P
I used to play HL2 on it, UT2004, Oblivion, World of Warcraft, Microsoft Flight Sim with 3 monitors and 2x graphics cards, Fear, did Cubase recordings of up to 47 tracks with moderate plugin usage, photoshop..the list goes on.
Ive currently got Reason installed on it, and Cubase, and a bunch of media. :) So as a spare media machine, or a spare World of Warcraft machine, it is still fine. Copy speed of about 60-90MB/sec from drive to drive on PATA, 4 drives and 2x DVD writers.that write at full speed simultaneously. And on 1.5GB of RAM.