After creating a new user and logging in as the new user, run iPhoto, go to "Share/Homepage" or hit the Homepage icon, and the new themes will download. You do not have to go on to publish, but iPhoto will be fixed. Go back to your original user account, and all will be well.
[robg adds: In browsing the linked discussion, there are a number of people reporting this problem, and a number of suggested solutions. If you're having trouble posting iPhotos to your .Mac homepage, it's worth a read (and there are a couple of other linked discussions from that one which may have further ideas). I don't use iPhoto to publish to .Mac, so I can't verify the problem or the solution.]

