List box problem

Hi,
Well, having made a fool of myself ( and probably upset Jubba into the bargain) in the clock thread, can somebody help me with a component problem I am having. I have looked at the tutes here ( and everywhere) for customizing components, but I cannot seem to get this.
Problem: I have a list box with 40 items loaded in using LoadVars( from a txt file), when an item is clicked it is highlighted ( so far so good), however, as it is multiple choice, I want the item clicked to stay highlighted when subseqent items are clicked - so the user cannot click the same item twice - any ideas ?
I will post a stripped down file if anyone wants to take a look

Cheers

SteveD