A VMware virtual machine disk is made up of two files: the .vmdk file and the -flat.vmdk file. The .vmdk file is the descriptor file and the -flat.vmdk file contains the data. If you have the -flat.vmdk file you can recreate the descriptor file using vmkfstools. This VMware KB: Recreating a missing virtual machine disk descriptor file (1002511) walks through the process.
This just saved my butt (again, but it has been awhile) so putting it here for future reference.
