Custom SID

To make a long story short, I have a situation where a certain percentage of systems in the field have varying SIDs (most are imaged, but some have been reinstalled from the XP cd in the field). About 30-40 of 200+ have SIDs to be changed.

My issue is that I need all of these systems in the field to have the same SID. Just the opposite of what has already been discussed.

Any suggestions?
Scripting this in would be a plus.