Cannot use or update WMware Fusion in Mountain Lion
The latest version of VMWare Fusion is version 4. If you want to use VMWare on Mountain Lion, unfortunately you can no longer use the old version. This VMWare blog post says:


  Does VMware Fusion 3 work with Mountain Lion?
  
  No. VMware Fusion 3 was released in October 2009 and was optimized for Mac OS X Leopard and Snow Leopard.  VMware Fusion 3 is no longer being updated for newer versions of Mac OS. Customers wishing to run VMware Fusion on Mountain Lion should use VMware Fusion 4. A free 30-day trial is available for current VMware Fusion 3 users. The trial can be found here: http://www.vmware.com/go/tryfusion