I just spent quite a bit of time trying to figure out why my vm's running on VMWare Server 2 had no network access. They would obtain an IP address from my network like they should, but I could not ping any machine on my network or on the Internet from those boxes and none of my boxes could ping the VM's.
After many hours of fiddling around and trying several different things, I remembered that I had installed Sun VirtualBox. I noticed this because one of the network adapters was for the VirtualBox installation.
On a hunch, I uninstalled VirtualBox. After a reboot, VMWare Server 2 was happy again. I don't know the details, but since I did not find anything while searching Google, I thought I should put it out there.