There is a diagonal line pattern tut over at 13 dots on this.
First follow trough with the tutorial.
http://www.13dots.co...showtopic=11852
You will have a 400x400 canvas with a orange background.
Now scale the canvas down under Image<Image size uniformly until you have the size of the lines you want. Also if wou want the lines to be another with you can edit the with settings of the rectangles to thicker or thiner.
Merge the layers with the rectangles (ctrl-e) and delete the layer with the background color.
Draw a rectangular marquee over your whole canvas and go under edit<define pattern... then save it with the name of your choice and it will become selectable as a pattern.