I can only assume that there is something on that drive that is 'in use' by the fully functioning new cloned XP installation? Some TSR or whatever? Something that either you or it installed there at some time. It will be a long haul to eliminate the problem. We all suffer from 'clutter' accumulated over the life of a drive.
Assuming you have looked through the start-up sequence in MSConfig (and the registry 'run'?), I would start by renaming ALL the sub-folders on the 'old' drive by adding some letters like 'bak' in their filename. Hopefully something will pop up and say you cannot rename as the file is in use. If that does not happen, try 'cut and paste' each of the files in the root directory to a new folder and look for the same message. there are some free/shareware progs which will analyse your start-up as well. Maybe they are listed at the forum top?