Here is a video tutorial in order to set up your Website Browse
. In your case you will use the Combobox to store the values instead of the Listbox.
Once you have finished the initial setup go to the ISS page and click on the Web Site Browser you created. In "Data Output" add a property with the following Binding Type: Physical Path. Now go to the dialog that contains your combobox and on the Next button add the following Published Event
Control Event: Set installer property value
Argument:The property you set to store the Physical Path
Now you should have the installation path set to the physical path of the web site.