jquery autocomplete - need to update one field as the user is typing in another field

jquery autocomplete - need to update one field as the user is typing in another field

I've got a username and id field.  Right now the admin starts typing a username into the username field and the autocomplete plugin starts displaying usernames that match.  That part works ok.  The problem is that the users id field is not presented correctly until the admin either finishes typing the username or selects a username and presses the TAB key. They do not want to have to press the TAB key - they want the id field to automagically update as they type, or when they select the username (NOT when they hit TAB as they leave the username field).

Is there a way to do this using the autocomplete jquery plugin?  Everything works now, but only if the admin hits the TAB key, which they don't want to do..... (and I need to do what they ask).