I upgraded by creating a backup of 6.01-01, installing 7.4 clean, and restoring from the backup.
The only thing I have found in the forums are registry settings that I would have implemented several years ago to attach them to the domain on the 6.01-01. I also notice that the registry settings mentioned include more than the one in the reg file that comes with SME. Not sure if that makes a difference, but I implemented all of them a while ago.
Interestingly, if I set security on a file in XP, I can query and see all users (including a newly created one). However, I could not log in as the newly created user.