What I need to do is create a 400 X 400 grid of squares, with coordinates for each square, I also need each square to be quite small say 15x15 pixels. I can't think of a non-tedious way to do this can anyone give me some advice?

It would probably be easiest to create the grid with programming. Maybe JacaScript of a server side language like PHP or ASP.

If I'm guessing right you're planning one of those pixel advertising sites in which case you may want to look into doing something else. Those sites are really just a quick fad and new ones seem to launch daily. I don't believe any other than the first few made any money worth talking about.

I'f I guessed wrong then nevermind, but still look for a prgramming language to create the grid. Which one you choose would depend on what you want to do with the grid.