Despite what Microsoft has stated you need to generate a new SID when using Windows 2008 images. On Windows 2008, you can use the native sysprep.exe utility. Note that running sysprep.exe will reset your hostname, IP and local Administrator password. When done generating a new SID you have to change your hostname, password and set your IP. If you want to see the before and after SID, download the PStools package at the URL below and run psgetsid.exe before you sysprep and then after.
1) Open Windows explorer and browse to C:\Windows\System32\sysprep and double-click sysprep.exe.
2) Make sure the Generalize option is checked under System Cleanup Action and click OK.
3) When the system reboots it automatically prepares it for first use.
4) On the Windows Setup screen, select your county, language and click Next.
5) Accept the license and click Start.
6) Click OK to set the local Administrator password.
7) Enter a password and click the blue arrow to complete the setup. The system will log you in. Make sure you change your hostname and IP before you join the domain. Also, if the old server object is still in AD, delete it before joining the domain.