not prompting for password access server

So I installed Vista Beta 2. I did NOT join this to the domain. I used the same username as a username on the domain with the same password. I goto run and type \\servername It is not prompting for a password, it just passes right through. I tried changing the password on the vista machine and doing the same thing. I then get a logon window. Is this some kind of new feature.. if so.. I think it is dumb. I also created another account to try this again to confirm. Same results.