Is the windows 7 vm running fine on parallels? If yes, you can actually convert the windows 7.pvm into parallels by using the import feature in fusion.
Now few things are not clear though, is windows 7 vm created based on boot camp or as regular vm? Can you check the size of vm and revert? Please go to following location
/documents/parallels/
in this location you must find windows7.pvm file. Whats the size of this file?