Hehe, i always liked this effect, that's why you can find it in many of my creations
There are at least two ways to do this:
1. Set the foreground color to black and background color to white, create new empty layer ovet the one you wish to interlace, then Filters > Sketch > Halftone pattern... > Pattern type: Line.
You should catch up from there and fiddle with the settings to make it look as you wish.
When you're ready hit OK, and set the layer transparency to Multiply to remove the white color.
2. Create new document with Background contents set to Transparent, start with 2x1px if you would like to make the line 1px high, 4x1 if your want 2px high line (and so on) and simply draw 1,2... pixels using pencil tool. When your tile is ready go to Edit > Define pattern..., name it, save it and now you can use it as Pattern Overlay in Layer Style window (after setting Fill to 0%).
The second method is more elastic, as it allows you to easily create whatever line pattern you like - horizontal lines, vertical and diagonal lines, or even black & yellow warning pattern, and then modify freely it's scale and transparency in the Layer Style window
It's definitely a good way to "darken" the backgrounds and make them less "flat".
By the way, how do you like the main screen? :>
P.S. I would gladly contribute my work to EECHC if you'll ever need help with gfx.