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I felt a bit silly doing it, but I ended up just doing a copy / paste from a simple directory listing of filenames into an Excel spreadsheet. Then it was a simple forumula to create the SQL insert commands. Another copy/paste into myPHPadmin and all set to go.
And if you want, you can put the system avatars in a subdirectory of uploads. Just put the filename in the database as "subdir/filename.gif" Works like a charm and keeps everything neat.