I have a hard time believing that you are running 5 boxes, especially the slaves at 800:600, unless you have them maxfpsbk at 1.

2gb was not enough for me when I was going through major cities, do the math though. WoW requires a minimum of 512mb, your running 5 of them, addons take up more, I'd say at a minimum for multiboxing you should have 3gb.

512mb
512mb
512mb
512mb
512mb
(256mb)XP
(1024mb)Vista

So
3.5 for Vista
and
2.75 for XP
MINIMUM.

Anyways, I'll need screenshots of leggs comp to believe him. Mainly because my old comp had barely any differences to his set-up.

My old comp:
Intel Core2Duo E6320
-2x1024Mb DDR2 PC6400
-1x250gb WD 8MB Sata (Contained all 5 WOW Clients, Separate folders)
-1x60gb WD 8MB System disk
-NVIDIA GeForce 7800GS Pci-E 256MB
-Windows XP SP3 (Never used it while playing)
-Acer 22" Widescreen

EDIT:
Reading his other posts I figured it out, he was doing the same thing that I used to, the in game size is set to 800x600, but he resizes them all the way down as far as they go. Which did work for me, but I like seeing.