Well ... it depends where your data comes from !
Supposing you have etxernal data to which you get access by a query
connection (for example webservices or sharepoint lists ...), you have to
specify this in the property page of the dropwodn control.
Then you can choose which repeating element you want to use as a source,
also indicating the value and the display fields.
For example if you connect to s SP list you tipically use the ID as the
value field and later choose an appropriate field to be displayed as a drop
down list item.
Finally, you have to "execute the query", triggered by the action you need
(might be an action on a button or just during for load).
I suggest you to use rules for this query invocation, unless you need
specific behaviour that you can get only by writing code.
If you use rules, you just add a "Query using a daa connection" action,
choosing the DC you configured as the source for the ddl.
Also, note that this way you can also pass parameters to the query (setting
the query connection query fields, if any) and have the resulting items
filtered based on your application criteria.
HTH
Ciao
Claudio Brotto
MCT - MCSD.NET - MCTS SharePoint
http://www.devlizard.com