Most INS systems can update themselves from VOR/VOR, VOR/DME, DME/DME etc.
DME/DME is generally the preferred method since it is far more accurate than any other fix method.
By the way, twisted - McD is a PPRuNe Moderator. Surprised you haven't come across her before. She is known, liked and respected by the vast majority of PPRuNers who have encountered her, both here and face to face. I'll stake a fair amount of my salary that 411A's post warranted the edit.