CF8 & AJAX to populate form fields

["cf8_user"]

First - I apologize if I am posting in the wrong area.  This is my first post 
and I am learning.

 Second - any and all help/info is greatly appreciated

 Now for my question...
 Everyone is talking about AJAX as a way to populate select lists based on what 
is 'selected' from another list.  My question is can this same concept be used 
to populate form fields?

 Case in point:
 A user is presented with a select list of user names; upon selecting a user 
name, form fields for
 1. Title
 2. Phone
 3. Email
 etc etc need to be populated without refreshing the page.

 Originally, it was thought we could bring all the "user data" in when the page 
initially loads, however, our user list has grown to over 4500 and is updated 
almost daily.  So bringing all that data in is REALLY slowing things down.

 The idea now is to create the user select list using only the user_id and 
user_fullname and upon change using the user_id to make a call back to the DB 
to get user data (title, phone, email etc).

 Can this be done with AJAX?  Would using AJAX be the best way to go?

 Any suggestions??

 Thank you...