I really don't think you want to try that using a trigger. It sounds like a really bad idea to me.
First and foremost, I don't know of any way to launch a trigger on a login or logout event. You could probably approximate this using either SQL Profiler or a "watchdog" process, but the fundamental idea isn't supported by SQL Server itself, so you'll need some kind of "helper" to get the job done.
Next, I'd be really leary of having users created "on the fly" by anyone, much less what you seem to be describing where every login has the ability to create users! I can't imagine a scenario where that idea would appeal to me, unless it was to torment some dba that was going to inherit that code after I'd left. The thought positively gives me the willies!
The temp tables really aren't any problem... SQL Server simply drops temp tables after the user logs off. You really don't need to do any "care and feeding" of them, they are completely expendable.
If you can explain what you are trying to do (in English, not Transact-SQL), I'd be willing to bet that someone here can offer you some ideas that will help a bunch!