phptemplate_username()

Hi!
I´m working on a social networking site (petlove.eu), and think this is a very nice and usefull module.
My support request is: I´m trying to figure out what functions i have to modify to theme all usernames that the module outputs. Other modules i´m using use the phptemplate_username(); function for usernames output. Could you point me out where to look?
Thanks!