Took delivery of 4 old CALL machines to add in to the labs.
Started a new build on one of them using my shiny new SP3 install disk.
Did some big updates to existing build and pulled it for rollout next week.

Follow-up: The next stage in the process was to place the updated ghost image on the new machines. I figured that I'd boot in to BartPE and pull the file from the USB drive; Bart refused to talk to the USB drive at all.

I also tried to install a clean copy of SP3 (my slipstreamed build) but it coughed up a hairball (BSOD) because of an error like this.

I eventually burned the ghost image to a DVD, booted BartPE and used the external DVD drive to read the ghost image.

UPDATE: all systems functional