Restricting usernames concerning capital letters

[Johannes de Le?n]

Well, I have been searching, without much luck, for an hack that doesn't allow a user to register with: USER NUMBER 1, but allows User Number 1. Any help concerning this?

It would be even better if it changed automatically.

I noticed when one posts a thread , if the title is all in Capital letters vBulletin already handles this, so, perhaps implementing that system into the registration form would do, just a guess.