[Windows Vista] What are the settings to log on automatically when Windows is started?

If Windows Vista meets the following conditions, it will log on automatically.
• One user account exists. 
•T he password has not been set in the user account.

If the above conditions are not met, please refer to the following:
1. Click START, and input control  userpasswords2 in the column of Search, and then press Enter key.

2. After displaying the User Account Control message, click the Continue button.

*For standard users, please see this FAQ - [Windows Vista] About User Account Control

3.

4. When Users must enter a user name and password to use this computer is selected, choose the users from the list of Users for this computer to grant access to this computer. 

5. Disable the Users must enter a user name and password to use this computer option, click the OK button.

6. After the Automatically Log On window is displayed, input the User Name, Password, and Confirm password.

7. Input the Password, and Confirm password when the account password is set.

8. Click the OK button. 
Press Ctrl + Alt + Delete when logging on to Windows Vista.
Related article:

[Windows Vista] How to change and delete password.
[Windows Vista] How to create and set new user accounts.