My 5 box experiment

[Xzin]

6600+, 7600+ all work great.. 8500 I think you will be disappointed with. 8600 or better, especially if you want to run 4 WoWs on 1 machine - WoW is mostly GPU limited.

[Kruiik]

Kruiik:
That being said, if I could run the one client on my 22" LCD and offload the other 4 clients to the CRT that's sitting next to it (also 22", 1600x1200 native resolution) that's currently unused, I could probably solve the problem. Also, 4 800x600 clients would fit perfectly with no unused real estate.

Then, all that would remain would be to find some sort of key broadcasting solution for the other 4 clients.

Actually this could be done with 2 monitors, and with some shell-bashing.
Nvidia-display card most likely required,though - but who buys CrapAti's anyway

X1 = Desktop + main WoW
X2 = 2nd X-server with 1600x1200 resolution on another monitor with 4 clients.

Hardware needed - Logitech G15-keyboard, or something with extra keys and Linux support.

Software XVKBD (case1) or Synergy (case2)

Case1:
Set up your normal single player stuff on X1, and do macros for everything you need on X2. Configure G15 (and G15 listener would be started in X2) keys to start xvkbd -text from shell (i.e. xvkbd -text AA - which would press shift+a twice in X2).
Create shell script so that you command actual script from G15, and script sends xvkbd-command to each 4 screens separately (-windowname parameter)

Make shellscript "pushkey" what takes keystrokes as parameters and send them to corresponding window.

voila, you can control your primary char normally - and use G15 extra keys to control each and every one of the dps-group you have behind you.
This is very similar to method i used to dualbox.

Case2:
I'm a bit unsure about this but you could install synergy on X1 and X2-5 - and use it to multibox, just give X-server different IP.

Case1 is definetly doable with 1 linux PC and with 1 or multiple monitors.