Automate Logoff - logon process and vice vers

Often in automation we have to deal with login to a system then logoff automatically and again login automatically. So hare I am posting ways to achive Logoff -> login automation.
- One thing one should know is even after system logoff there are process which are still executing. These process are background process or windows services.
So the trick is create an windows services or create a background process and then logoff. Now using this process you can do anything like login through windows UI using windows automation model or write a code to stimulate auto logon.
Reference link for creating service for remote sys is : http://support.microsoft.com/?kbid=251192
See also : How to logon automatically on windows startup:
open registry - HKLM->Software->Microsoft->WindowsNT->Winlogon and update the following kyes- DefaultUserName, DefaultDomainName, DefaultPassword with the logon information.