I know this post is old, but I wanted to add something I have had to do in SQL 2005.
After using sp_reassign_dtspackageowner, I had sucessfully changed the owner, but my user still could not save/create new versions of the DTS.
I found that in msdb.sysdtspackages, her login name was in 'owner' correctly but not in 'owner_sid'. So what I had to do was retrieve her sid from msdb.sysusers, and then execute this one-
update sysdtspackages set owner_sid = her sid where owner like 'Her Login';
Now she can edit and save DTS packages.