Making a Grid

Open up a 10 px. X 10 px. document with a black background. Then, increase the magnification to 6400% by hitting Ctrl + +. (The other plus is the plus button near your backspace key). Also, make your rulers visible, by hitting Ctrl + Alt + R.

Using the marquee tool, select out a section of the square that is one pixel away from the side, and one pixel away from the top. Use the crosshairs with the rulers to achieve the one pixel boundaries.

Fill the selection with white, and then decrease the magnification back to 100% by pressing Ctrl + -. Your image should look like the one at the left (the gray background is from the Fireworks background).

Now, go to File - Save As and save your image as a grid.png. To apply the grid pattern, open up an image. Then go to the fill tab, select pattern from the dropdown menu, then choose other. Load the grid pattern (grid.png).

Use the paintbucket tool in order to fill your image with the grid patter. You're done!