In Vista if you do a clean install (not an upgrade), this account has been disabled by default. If for some reason you need to reactivate this account (which I recommend against unless there is a good reason) the instructions are below:
- Log on to the machine with a local administrator account (if you don't have one already then these instructions will not work for you).
- In the Search field under the Start menu type MMC.EXE and press the Enter key. Press Continue button in the UAC prompt to open the console.
- From the File menu, select "Add/Remove Snap-in".
- In the "Available Snap-ins" list on the left, scroll down and select "Local Users and Groups", then press the Add button.
- In the "Choose Target Machine" dialog box, select "Local Computer" press the Finish button, then press the OK button.
- Expand the "Local Users and Groups" icon in the left pane and click the Users folder.
- In the right pane, right-click Administrator account and select Properties
- In the General tab, uncheck "Account is disabled" box, then press the OK button.