Sure, I came across it while attempting to create patterns.

Open a new document transparent width (in pixels): 7, and length: 4

Zoom in all the way, until you basically get 8 lines of squares.

Take the pencil tool, and fill the first square rows, the in desired scan line colour, (from the top) so that you have created it 1/4 full. Alternately, for thicker lines, fill more rows.

Then select Edit>>Define pattern and save it.

Go to your image where you want the scan lines, and select EDIT>>FILL and change the option to "pattern" then select your pattern you just created .

Ta da!
Photoshop can do incredible things... this is only the 3rd day im using it O_o. Too much to fgure out ^_^ *brain hurts*