How to explicitly set a drop down listbox item?

I have a drop down listbox with 5 names in it. Each name corresponds to a team name, and each
team name has a number associated with it. What I do is point my drop down listbox data source at the
following XML file and all works great:
<?xml version="1.0" encoding="utf-8" ?>
<Root>
  <Field text="Chargers" value="1"></Field>
  <Field text="Seahawks" value="2"></Field>
  <Field text="Giants" value="3"></Field>
  <Field text="Dolphins" value="4"></Field>
  <Field text="Cowboys" value="5"></Field>
 </Root>
Sometimes I need to explicitly set the selected item in my drop down listbox, but I don't know how
to do that. For example if I want to explicitly set my selected drop down listbox it ...