To get your VSS password & user ID auto-entered by VSS you need to define environment variables that contain this info.Here is how to do it:
1. Right-click My Computer and then click Properties.
2. In the System Properties dialog box, click Advanced, and then click Environment Variables.
3. Under User variables click New.
4. In the New User Variable dialog box, in the Variable name box, type "SSUSER".
5. In the Variable Value box, type your VSS username, and then click Ok.
6. Repeat these steps to add "SSPWD" as an environment variable whose value is your VSS password.