if you use firefox an easy way of getting the current url is to go to google maps and then open "Tools -> Page Info". Under the Media tab you can then see the urls for each square on the map.

Then just remove the number after mt and replace the x, y and zoom values with %d to get:
http://mt.google.com/mt?n=404&v=w2.17&x=%d&y=%d&zoom=%d

looks like the one in the earlier post had an extra % in there