I have a dual Atlhon 2600+ (2x 2ghz bartons) w/1 GB of ram and a few SCSI drives and 2 LCD monitors.
I do a load of stuff at once. at any given time I may have 10 IE windows, Outlook which has 12 email boxes open, mIRC, Photoshop and/or Adobe Premiere running, trillian, DVD Shrink running (I "archive" DVD's on a daily basis), Ultra Edit with between 10 and 20 docs open, WSFTP, SecureCRT,sometimes a VMware session I use for VPN into work, a couple termininal services windows to servers in my apartment. Windows media player open some of the time, My memory load on the box when nothing special is going on is like 700MB of ram used hehe. The machine just never hiccups, glitches, crashes, or slows down unless I screw something up.
I have been running DVD Shrink while playing Doom3 already with minimal impact on the game. 2x CPU's = 2x the Love