I  have  experienced much trouble with running Virtual machines on VMWare Server 2.

The randomly froze and even the host server was unresponsive at times.

When I logged into the VMware remote console there were details like

sd 0:0:0:0 or so which meant that the VM struggled to read/write to the Virtual Disk.

The first thing I did was to install VMWARE tools again and it helped a little.

The ultimate  solution I found was to change the Disk strategy from DATA SAFETY to PERFORMANCE.

This really worked perfectly and the VM’s never froze again.