You can do this by setting a rule on the drop down list.
Open the properties for the drop down list.
The data tab should be selected.
Click Rules
Click Add.  You can give the rule a descripting name (Rule1 is the default)
Click Add Action.
Select Set a Fields Value
Use the Field chooser button to select the text box.
Use the Value button to reference the value returned by the drop down (this
should just be '.')
Click OK four times.

Now when you select an item in the list, the underlying value of that list
item will appear in the text box.

HTH,

Jay

Hi Mike,

You can do it by code.  If your textbox is named: field1, you need to use:
IXMLDOMNode oNode1  = e.Source.selectSingleNode("my:field1") to target the
correct textbox in a repeating section.
If your drop-down is field2 (IXMLDOMNode oNode2  =
e.Source.selectSingleNode("my:field2") )
then, field1.text = field2.text;
Your code can be placed on the OnAfterChange event of your field2.

Again, the trick is to use e.Source.selectSingleNode("my:field") instead of:
e.XDocument.DOM.selectSingleNode("//my:.../my:field").

Hope that it helps.

Franck Dauché