$+(something,somethingelse,andonemorething) joines them together into somethingsomethingelseandonemorething
But your example wont work becuase you cant just stick " on the front and end of a $+( ) like that.
You can however put them on the inside.
$+(",$scriptdir,Themes\vtecGOLD.mrc")
becuase then they become part of what your joining up. (concatanating)