Weird graphics crash while 4 on 1 boxing.

Hello.

My setup is two PC's for 5 boxing.

PC for main character:
- WinXP pro 32-bit
- E6600
- 2GB PC6400 DDR2
- 8800 GT 512 MB
- 250 GB HDD for WoW client

This box runs my warrior which is my main while multiboxing. This box is OK, so settings are irrelevant.

Second PC:
- WinXP pro 32-bit
- Q6600
- 4GB PC6400 DDR2 (i know about the 3gb limit)
- 8800GTX 768MB from Asus
- 2x250 and 1x500 GB HDD for 4 WoW clients

This box runs my 2xmages, 1xwarlock and 1xpriest. This box poses the problem. I run the four clients via keyclone on a 22" widescreen (1680x1050) each using 1/4 of screen real estate. All graphics are low and i use keyclone to set FPS to 15-30.

Example: while flying around Outland, sometimes the screens of some of my boxes display a chaotic array of colored triangles, completely visually screwed up. I am able to restart the clients, but the best thing to do is to reboot my pc entirely. I presume to clear the memories of the components. This happens frequently while running 4 clients on this PC. It sometimes also happens when 2-boxing on this pc with very high settings on both clients. It does not matter wether I use multisampling or not, it crashes rarely on both occassions. Before, I 5 boxed on this machine with the same crash happening. Thats why i brought out my old PC. I use Multibox software for the PCs.

So while running 4 clients, the graphic crash happens frequently, like while flying over graphically intensive areas such as shattrath or terrokar forest area. While 2-boxing with high settings, the crash happens rarely.

The temperature of the card never exceeds 70 degrees celsius, while idle temps are 60-ish. I presume to rule out overheating.

This quad core pc runs single 3D-applications perfectly, like Crysis on high, STALKER on high etc etc. No problems with WoW either when running just the one client. But as soon as I run multiple clients, the problems start. The problem only occurs in WoW AFAIK, since I dont multibox anything else.

I use the latest drivers from the nvidia site.
CPU and RAM usage is way low, never over 50%.

So my question is: does anyone recognise this or has any theories regarding the problem? Also, I have Vista Ultimate 64-bit lying around and havent tried that one for the 4 boxes. Would it improve? Im kinda at a loss here since its ruining my multibox experience. I can do several Daily quests or an instance with no problems, but as soon as I fly out in the Outland world, a crash is bound to happen.

Regards, Zuvio.