Well I need client side scripting. So i guess I wouldn't be using AJAX.
By type ahead I mean an implementation as we see in our MS outlook where we have to search for a contact. For eg. I have a drop down list in my drop down List (from <input type="dropdown"/>
and if my list is 100 items long, I dont want to scroll down the entire list to find a name. I would prefer to type the name in the Drop down menu(similar to the way we type in our browser and get a auto-type ahead) and that would pull up the name from the list.