I know that with video files at least, windows makes DLL calls to "analyze" them to generate "multimedia" info for various explorer columns, some of which might even not be currently active. If the file is corrupted/truncated, and the decoder for that particular video file doesn't handle this well, it can really slow down and/or crash explorer.exe.

Something similar might be happening with the pictures.

I've noted that now that I have iView set to be my standard app under XP and 2K for viewing/editing pics, all the previews generated have the iview logo stamped on them.

That's evidence that the 2K/XP preview function is calling the "owner" of the file type to do the processing.

Perhaps the owner of the image file types in question is having problems with some of the images?