A nice article on setting up a malware analysis system (packet sniffer, firewall, WinDiff,..) under VirtualPC.

Capture, care and analysis of Malware made easy

http://www.linklogger.com/vm_capture.htm

Kayaker

Is WinDiff only for Virtual PC?

No, it comes with Visual Studio: http://en.wikipedia.org/wiki/WinDiff

check KDiff3 out, too

I mean if i can use it with VMWare
I think i should try it with VMWare myself as far as i see now it is a program that find changes vs two drives, i first though it scanned two Virtual PC images :S