Determine which item in a list box was chosen?

How do you determine how far down the list in a combo box the user went before selecting an item? For example, if there are 10 account numbers when the user clicks on the list box and he selected the 3rd one down, is there any way to record the 3?

Also, my userform works fine if the user selects any of the items in the combo box besides the 1st one, because I have it set to sub Processs_AfterUpdate

When I try to have it execute using other events it either executes before I have a chance to select anything else, or it won't execute at all (like with the After_Update)