INSERT INTO snapinAssoc (saHostID,saSnapinID) SELECT hostID,122 FROM hosts WHERE hostOS=‘1’
This will only work on FOG <1.0, but here it is, in case anybody is searching the forum for something similar. In this case, my saSnapinID is 122, and we were looking for all hosts with a hostOS of 1 (which was XP).
Thanks to Tom for all of his help!