Hey I'm very new to multi-boxing, and realized since I don't have the money to go out and buy 4 extra computers, I'll just upgrade and multi-instance. Though I'm not very experienced when it comes to the necessary computer hardware.

My current setup is:

Dell XPS 400
Intel Pentium D CPU 2.80 GHz
1024 MB RAM
nVidia GeForce 7600 GS 512 MB

I just ordered another 2 gigs of RAM, but what else should I be looking to upgrade? I want to 5-box with keyclone on the same computer, but I don't exactly know what I need. I was able to run 3 WoWs with 50-95% usage, and FPS jumping from 8-35 on each, though I haven't been able to try 4-5. Any help would be great. Thanks.

Edit: My budget is not extremely high so I don't need the top of the line hardware, though I do want to buy good hardware that will last for a while. Also I might be willing to buy another monitor if its worth it.