Since your Media Center is set up to be an appliance, there’s no need to login every time it boots. Although it will automatically login if you leave your password blank, the default network policy will not map network drives with blank passwords. With Windows XP I used TweakUI to automatically login, but now Vista lets you do this without additional software.
Go to the Start Menu, type netplwiz in the search box, and press Enter If you have UAC active (which you should), you’ll need to give permission for the program to start.
The User Accounts window will open. Notice the option Users must enter a name and password to use this computer, uncheck the box and click OK.
You will be prompted for the login name and password of the user that you want automatically logged in. Enter the information for a user account that already exists and click OK.
Now Vista will automatically login without any user intervention!
You should always have a password assigned, even if you are automatically logging in, to help prevent remote access to your machine If your machine is physically accessible to others, setting your machine to automatically login will allow them the same access that you have.