User Interface question

I have a text input box that auto-completes. When the user hits tab or enter, that item is added to a list. As it stands now, the item ALSO stays in the text box, and the user has to backspace/delete that item before typing in something new.

My question is, how can I remove the item from the text input box without jolting/confusing the user ? The target group won’t be very experienced users, so I’d like some sort of transition from hitting enter to clearing the textbox for them.

Any ideas ?

Also, are there any forums specific to user interface design that someone could recommend ?

What script language are you using?