ive got 512, and that runs YIM perfectly... and i normally have AIM, YIM and MSN running at the same time, i talk to different people on each... absolutley no probs running them all together, and normally itunes, and firefox... doesnt even run slow...
I normally run about 10 tabs on avant, windows media player, msn, outlook 2003 (1/5th the time) and occasionally photoshop cs 8 and sonicstage mp3 player manager.
I usually have Firefox with four to ten tabs open, Windows Media Player 10, AIM Triton, MSN Messenger and various other things depending on what I'm doing.