Hi kbrocksi,
What u have to do is...
First add a dropdown list to ur form.
Now u will have a field say field1 in the main datasource.
Double click the field1 in the datasource task pane to view the "Field or Group Properties" dialog box.
There is an option to specify the default value.
After specifying the default value,close the dialog box.
Now double click the dropdown in the InfoPath design.
The dropdownlistbox properties dialog opens.
In the dataconnection dropdown, select/Add the dataconnection.
When u preview the form,the default value will be set in the dropdown.
Regards,
Abhishek