Formatting Usernames

[pplc]

I would like to setup new registrations to require a first name and last name so their username would be like "Jane Smith". Is there anything out there that would ask them for their first name and last name and automatically create the username from that? At this point I would settle for them inputting it in themselves just a first and last name in as their username but I'm not sure how to require it. I saw there was an option to user a Regular Expression in the username field but I just don't understand it and I am not even sure if that is what I need to use. But inputting a first and last name and automating the username would be wonderful!