[WoW] Crashing while alt+tabbing 2 accounts on 1 pc

Hello everyone. This is my first post here and im pretty new to all this so please be kind. =)

I'm attempting to run 2 copies of WoW on 1 pc. Each account is run from a seperate installation of WoW. I am not using any special software, just alt+tabbing back and forth as needed.

The problem I am having is sometimes while alt tabbing back and forth one of the copies of WoW will crash out giving me some d3d errors.

My system specs:

AMD 64 4000+
Geforce 7800 GTX
2g Ram
74g Raptor Hard Drive

Yes I know its not the best in the world but its all I have at the moment.

Would it be better to run WoW in windowed mode?

Is there some form of 3rd party software which would limit how much video memory each instance of WoW uses?

Thank you for taking the time to read this and for any/all replies.

Try keeping your second box minimized at all times unless you need to view it, that will greatly reduce the GPU / CPU load aswell as RAM usage, see if that serves you any justice.

Other than that look at your graphics settings per wow instance you have open, check that all the special details are turned off and you are running windowed at the lowest res for best performance.

also make sure your sound is not doing hardware acceleration and not in the background