How do I fill an area with a criss-cross pattern in photoshop cs5?

I’m not sure what you mean, but I think if you select colors like grey and a darker shade and or black and foreground and background colors. Then under filter go to render clouds. This will make clouds from the two colors you previously selected. From here you can play a lot with trying had filters that give that criss-cross look you’re looking for. Try Cross hatch and or pixilating (experiment). Like I said though, I’m not exactly sure what you’re looking to do, so this might not help you at all, lol.

I’m not exactly sure what you are asking but I think this might be what you are looking for.

This is a 2X2 grid blown up to 3200%. You could use whatever size grid you needed. Now define it as a pattern.
http://i.imgur.com/7GZww.png

http://i.imgur.com/3UEKl.png

http://i.imgur.com/eKtBG.png

http://i.imgur.com/PR4s6.png

http://i.imgur.com/y5BS2.png

And it will fill inside the selection if you made one.

@Not_the_CIA Brilliant, thanks!