Dc++, Bittorrent, peerblocker, Kerio Firewall, deamon toolz, msn messenger.
Runs fine.
Here are some of my specs:
Cpu: 1400 mhz AMD athlon - Unclocked
Ram: 512mb
OS: Win XP SP1
Video Card: Geforce 4 64mb
Sound Card: Sound Blaster Live! series
Medium Detail, simple reflections, no anti-aliasing. 800 x 600 x 32.
HL2 runs perfect and looks awesome.