You may want to shut of UAC (User Account Control) first.
Copy the VGHD data directories (i.e. the entire VGHD folder with the sub folders) from where you have it to the other drive which would then be X:VGHD (where X is your other drive)
Uninstall VGHD and then reinstall and watch for the option to change the data directory, its not a prompt, just a section on the setup screen.
NB: The uninstall will removed your saved (and encrypted) password, so you either need to have remembered what your VGHD account password was or to check on your password at the following BEFORE you uninstall:
http://www75.virtuagirlhd.com/us/customerservice.php?csCatId=14&csQuestionId=125 When you browse to select the drive X, it will display the new destination as X:\. Do not worry about the second slash. You should then be right to re-update your rights and the models should not be redownloaded.