You can use the TextLine object from the Catalyst Library to do this:
IDL> text = Obj_New('TextLine', 'Sandy Cape', X=0.35, Y=0.85, Color='NAVY', $
Font=1, /Background, BG_Color='WHITE')
IDL> text -> Draw
You can find the Catalyst Library here:
http://www.idlcoyote.com/catalyst/catlib.html