How to process a selection in a listbox, and set a selection in code

I have listbox on a form in my VB 6.0 app.  I simply  need to be able to do two things:

 1) In my app, I keep track of what item is currently selected.  So, when the form is displayed, I need to highlight that item in the listbox.

2) Upon a list item selection, I need to immediately process the selection and update my dialog.

Thanks ahead of time.