You can do this using Advanced User (http://drupal.org/project/advuser) or, another option is to make a views (http://drupal.org/project/views) with an exposed filter, which would also let you search for users according to the parameters you allow (for example, username contains, or beggins with, or ends with etc).
Is there a module that lets me type in the username or last name of a
user in the admin so I can find someone without scrolling through
hundreds of pages of users?
"The only people for me are the mad ones, the ones who are mad to live, mad to talk, mad to be saved, desirous of everything at the same time, the ones who never yawn or say an uncommon-place thing, but burn, burn, burn like fabulous yellow roman candles." ~ Jack Kerouac