Instructions for Setting AutoAdminLogon

Launch Regedit. (See more details on starting regedit)
Navigate to:
HKLM\Software\Microsoft\Windows NT\CurrentVersion\winlogon 
Set: AutoAdminLogon = 1 (one means on, zero means off)
Tip: Try Regedit's 'Find': AutoAdminLogon
Create a new String Value called DefaultPassword
Set: DefaultPassword = "P@ssw0rd"
Check for the existence of a REG_SZ called DefaultUserName. The value should reflect the user who you wish to logon automatically. If this value does not exist, then right-click in the right pane, New, REG_SZ, name it, DefaultUserName. Set the string value to the required UserName.
Optional Item: If your Vista Machine has joined a domain, then create a String Value called DefaultDomainName.  
Set: DefaultDomainName = "OnlyYouKnowDomain"

Here is a summary of the four key registry settings:

"AutoAdminLogon"="1"
"DefaultUserName"="xxx"
"DefaultPassword"="xxxx0xxxx"
"DefaultDomainName"="xxx.xxx". Definitely needed in a domain situation.