Exactly, it might have been wise to upgrade the OS while you were doing..
When I upgraded to 2.4 dual core, 1Gb RAM, and the 200GB hardrive, I cloned the orginal drive with Ghost and used it as my master while copying the clone on to the new HD (slave). Then I removed the original drive and put the cloned 200HD in the master slot. No problems yet. Of course, I have had the same OS since XP came out, which Im sure made the transistion easier..