More detail (such as the data or surfaces themselves) would be helpful.
The approach I would use is to subtract one surface from the other. Where this is equal to 0 is where they intersect. An easy way to find the (x,y) coordinates of the intersection (when you have done the subtraction), is to use the contour (link) function to draw the contour of the result of the subtraction. Use the technique described in Contours at One Level (link), with the level defined as [0,0]. Also see the section on Output Arguments (link). You may have to experiment a bit, depending on how your surfaces are defined.
