I had a problem where I couldn't shutdown my Windows XP under VMWare Fusion - it started shutting down and then just locked up. There doesn't appear to be any way to force a shutdown via Fusion.
My solution, via Google, was:
1. Force quit VMWare Fusion and vmware-vmw (password required) via the Activity Monitor.
2. Goto to the Virtual Machine (eg. Documents/Virtual Machines/XP) and "Show Package Contents"
3. Find the file ending with ".vmem" and move it to the trash.
4. Restart the Virtual Machine and all should be good!
Well, it turns out there is an easy way to do this from the VMWare application itself. In the comments below, Ben from VMWare mentions that holding down the "Option" key while the Virtual Machine menu is open will change the "Shut Down Guest" to "Power Off". Nice!!