Vista - Password Protected Sharing is On, but I'm not prompted for a password

I am trying to share files on a Vista Home Premium x64 desktop with a Vista Business x64 laptop.

Network Discovery, File and Printer Sharing, Password Protected Sharing, and Windows Firewall are all ON on both machines. I am not using a 3rd Party Firewall. I am logging in with a DIFFERENT user name and password on each machine.

If I browse Network Explorer on my Business x64 laptop, I see the Home Premium x64 desktop machine, but when I double-click on it, all I see the printer. I am NOT prompted for a password, and as a result, I cannot see any of the shared folders.

If I try to access the Home Premium x64 desktop by typing its IP address into Network Explorer (instead of its machine name), I am prompted for a user name and password, and then I see all shares.

Why would this be happening??

The only way I can force the password prompt using a machine name is if I type the path of a known (but not yet visible) shared folder into Network Explorer. For example \\DESKTOP\Share01

Then it will prompt me for user name and password and open up the Share01 folder. It then also reveals all the other shared folders.

I need it to prompt me when I double-click on the machine name. Anyone know how to make this happen?

Thank you.