Here's a nice tutorial on scanlines. This was done in Photoshop CS2, it's good in previous versions.
Now, open up a new image, size it to 4x4 pixels, make sure it's transparent! Next, click the Zoom tool,

and zoom in by 1600%.
Now select the Pencil tool. Right Click the Brush Tool, not the Airbrush, the Regular Brush tool and select the Pencil tool.

Make sure it's on a 1px radius, and click the tool until it looks like this:
I used the color value
#000000, but you can choose what color you want your scanlines to be, but
#000000 is recommended.
No go to Edit>>>Define Pattern then call it scanlines, and you're done! You need this tutorial for the Basic Avatar Tutorial!