This tutorial who show you how to creat a simple Combo Box: dropdown1.swf 

1. Let’s start with a Flash document File > New > Select Flash Document > OK

2. Drag ComboBox from the components > User Interface into the work area

(under properties you can change the size of the combo box)

3. Let’s add some data to the combobox Select Parameters

4. On the Parameter box you should see  data, editable, labels, and rowCount (see screen shot)

5. Now select labels, and select this  should bring up and another windows, and it look like this one:

[ + ] allows you to add the label name
In this case I added RM Templates as value and in order number is 0

continue…