After slipstreaming Service Pack 3 into my Windows XP Professional CD image, you cannot use FAST (File and Settings Transfer Wizard) to import a backup made with FAST on a XP SP2. Attempting to do so will yield this error:
Your migration store was created with a previous version of File and Settings Transfer Wizard.
This is of course not very nice. Especially not if you reinstalled the machine in question.
The fix is to apply hotfix 896344 on the old XP SP2 machine, and then make a backup using FAST.
This backup will be suitable for restoration on a SP3 machine.
The microsoft page on this hotfix only mentions this issue to apply to x64 Edition, however is also applies to pre-SP3 versions of FAST.