It's easy, you should be able to just follow the model of the mod I made for this in YaBB SP1. Just add a new field to the members table for their template and have the forum open that template instead of the default one. Also have to add some code to profile to list all the templates available and some admin center options, like choosing the templates directory and allowing the admins to edit all the templates. Of course, don't forget error-checking in case the template ceases to exist or something.
