Thanks for that post, Doug.
I was having the same problem (IIS, Windows XP). The answer for me was that the php.ini (which must be stored in your windows directory, like c:\windows) referred to a upload_tmp_dir and a session.save_path to which IIS cannot possibly get access (because IIS runs using a user that is not the logged in user). So if you change those values to a normal directory the whole thing works.
Thanks for you help everybody. Now if I can only figure out how to get my Joomla to work on Godaddy Shared Hosting without switching to Linux... well, we shall see.
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