*sigh*
rightclick anywhere an the window (not over a combobox or checkbox or something, just the window).
There should popup a menu: http://www.erightsoft.net/snaps/images/rightclick.gif
And the topmost menu item is?
Right: ADD MULTIMEDIA FILE(S)
Or you drag a file from the windows explorer onto the super window where you can see the label "DRAOP VALID MULTIMEDIA FILE HERE".