As you know, we can use Newsid.exe tool ( http://technet.microsoft.com/en-us/sysinternals/bb897418.aspx ) to change the SID on computers, especially if you are working with virtual servers. But Newsid.exe tool doesn't work on Windows 2008. You can successfully change the SID on Windows 2008 using Newsid.exe tool but after the reboot you will get a Blue Screen. Also, keep in mind that Microsoft does not support the images that are prepared using Newsid.exe tool.
If you really want to change the SID on a Windows 2008 computer, you need to run Sysprep command. By default, which is located in c:\windows\system32\sysprep folder.
But Sysprep command won't work on an upgraded OS image. For example if you updated the image from Windows 2008 to Windows 2008 R2, the Sysprep command won't work. You will get the following error message:
This is because Microsoft does not support the use of Sysprep to create or modify images of an installation that has been upgraded. In this case your only option is to create a new image from scratch.