GE allows you to mark 2 points and draw a line between them (but no ability to place a grid on the map
)
Suggest you draw a 1000M (or whatever grid square you are interested in) at the top corner of the GM image. Save the image with the reference line. Now, import to paintshop pro or whatever - and use the reference line as the basis of a grid using the drawing tools??
Cheers
Andy