In just a few steps, we are going to create a grid pattern, excellent for use as a web background or as a topping for a Greek salad. In the Channels palette, create a new channel (Alpha 1), click on the newly created channel and use the pencil tool (hold down the Shift key while doing so) to create your lines.

Utilize the rectangular marquee tool to draw a selection around the intersecting lines. Go to Edit > Define Pattern. Deselect. Cntrl + Delete to clear the selection.

Go to the Layers Pallet and click once on the background layer. Use the Paint Bucket and under Fill, choose the pattern you just saved. Fill the image with the new pattern.

Use the Gradient Tool to brighten up the image, if so desired. And there you have it...