From http://www.vmware.com/products/beta/vmware_server/releasenotes_vmserver2.html:

On Linux, if you run vmware-uninstall.pl when virtual machines are running, the uninstall will fail and it will not be possible to shut down the virtual machines.
Workaround:
If you installed using tar:

1. Run /etc/init.d/vmware-mgmt restart to restart VMware services.
2. If neither xinetd nor inetd is running, run /usr/sbin/vmware-authdlauncher to restart the authorization service.
3. Log in to VI Web Access and shut down running virtual machines.
4. Re-run vmware-uninstall.pl.

If you installed using rpm:

1. Kill all vmnet-xxx and vmware-xxx processes.
2. Remove VMware Server files using the following commands:
   • rm -rf /etc/vmware
   • rm -rf /usr/bin/vmware
   • rm -f /lib/modules/`uname -r`/misc/vm*
   • rmmod vmnet
   • rmmod vmmon