I play my second character on an old laptop I scavenged from work. It's a 1.8GHz Centrino w/ Intel integrated video using 64MB shared memory of 768MB total. I've got the graphics turned to the lowest settings and the sound turned off. I haven't really noticed lag, even in Outlands.

You don't need a killer rig to run WoW. Now, I've got something very similiar to what you're looking at on my main system, but I use that for more than just WoW. I've toyed with the idea of running my secondary WoW accounts on virtual machines, but haven't taken the time to set it up. Anyone out there using VMs to run their other accounts?