Here's what I have so far...

Note I use *double click* to put stuff into the listbox. This is because the
click event is triggered when you select an item so we get in an endless
loop thingy. I'm trying to think of a way around this... Maybe use different
events for the controls... But I think otherwise it fits your bill.

I'm testing with a plain userform with one textbox txt1 and one listbox
lst1.