Help with virtual directories

[eluser]cmgmyr[/eluser]
Hello all,
Hopefully this will be a quick answer but I couldn't find it anywhere. I would like to do something like this:

domain.com/{username} (controller 1)
domain.com/{username}/controller2
domain.com/{username}/controller3

Example:
domain.com/cmgmyr (profile page)
domain.com/cmgmyr/friends
domain.com/cmgmyr/friends/add
domain.com/cmgmyr/music
domain.com/cmgmyr/music/vote

How do I set it up so that I can pass the user name to a function, get the userid, then pass that to the other controllers/functions?

Thanks in advance.
-Chris