as a work around, once you get to the "Select method for Mapping Users" screen.
-select "Generate a new mapping file"
-click browse, name the file, save and click import
then edit the XML file by putting in the domain and admin account you are installing it with. (best just to use the setup account for and then add other users once CRM is up and working)
-run the import org process again
-and select the "Use existing Mapping file"
-browse to the location you saved and proceed with the install