What I've taken to doing, is create a template map with a grid laid out on it already, sized at maximum of 256 x 256. Using the rectangle tool, I draw a black line every 20 steps. It takes a little time to set up initially, but then I just copy/paste the template when I need a new map, resize it accordingly, and it's ready to go. Did this in Ace too, didn't realize it had a built in grid. *sigh*