Well, the Zalman CNPS7000A-Cu is 109x109mm.. my guess from the looks of it is that the XP120 is along the lines of 125x100 excluding the heatpipes, or about 125x125mm including them. Since the heatsink flares up and out from quite a small base like the CNPS7000A-Cu, it should fit on most motherboards that the Zalman does, a list of which you can find
here for P4 motherboards and
here for Socket A motherboards.