A very simple approach would be:
1) Load the listbox with values
2) Use a Select Structure:
Select Case Listbox1.Value
Case "Hello" or "1234"
If you use a Forms Listbox then you'll probably need to run this code on a change event in the linked cell that is hooked up to the listbox (these are easier to set up and look better so I would go with the forms listboxes).
You can also run macros from the macro dialog box.
If you use a Forms listbox it's as easy as setting the link range. But since you are using two columns, you'll be best of creating a "third" range where all 20 cells are in order top to bottom (simple formulas will populate this from A1:B10).