Vista :How to Log on automatically
The procedure for automatically logging on to a default user account is essentially the same in Vista as it is in XP. First, the obligatory caveats and warnings:
Don't do this if your system contains confidential data and is physically insecure. It's a very bad idea to enable auto-logon on a notebook, for instance, because anyone who walks away with the notebook can get to its contents just by turning it on. The same is true if your system is in a location that can't be locked up, such as a cubicle in an office bullpen. A passerby who wants to break into your computer only has to hit the power switch and wait for your system to restart and log on automatically to your account.
Also, don't follow the instructions from some older Windows versions to enter your default password in the Registry. That option works but leaves your logon password exposed in clear text where anyone can find it. The option described here saves this value as an encrypted LSA secret, which is many times more secure.
As long as you understand and accept the risks, here's how to enable auto-logon (these steps work identically in all Vista editions, including Home Basic and Home Premium). These instructions assume you are using a workgroup configuration and not logging on to a Windows domain:
1. From an account in the Administrators group, click Start. In the search box, type netplwiz<> and press Enter. This opens the Advanced User Accounts Control Panel shown here. (Update: If you're trying to accomplish this in Windows XP, click Start, Run, and type control userpasswords2 in the Open box.)


2. Clear the check box to the left of Users must enter a user name and password to use this computer and then click Apply.
3. In the Automatically Log On dialog box, enter the user name assigned to the account you want to Windows to use each time you start up. Enter the password in both dialog boxes.


4. Click OK to save your changes.
Now restart your system. You should bypass the logon screen and go straight to your desktop, just as you did in XP.
For a little more control over the autologon process, including the ability to set up Autologon for a limited number of sessions, download the Autologon.exe command line utility, created by Microsoft developer Andrew Jennings. Usage instructions and some interesting comments are available in this post on the Microsoft Shell Blog.