Sorry I wasn't very clear on my problem.
Eric showed me how to get 2 columns to show in the combobox, but now I need to reference the first COLUMN not the first item. For example, if my combobox displayed the following:

0001    item1
0002    item2
0003    item3

I want to lookup values in "mytable" based on the first column.

select * from my table where id =  (column 1 of the selected list item)

In other words, if the user selected item2, I want to find a record in mytable where the id = 0002.