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#11
What you are saying is a little confusing so to be clear. I assume computer A is a Dell Latitude 810 with Windows 7 and B is a Dell Latitude 800 with XP.
You made a Macrium image of computer A. Swapped the computer B drive into computer A. Performed a system image restore to A. I would have expected A to boot because all you have done is replace the drive and reimaged. You can go down to the shop and buy a brand new drive and do the same thing. BTW this is not cloning.
The OEM:SLP is likely to be an issue if you put the computer A drive (810 pc) into the computer B (800 pc). There is a SLIC table in the BIOS used to authenticate licensing. If it worked and I was MS I'd be knocking on Dell's door.