Ok ,there are various ways to do it depending what sort of graphic manipulation software you use.
1) Photoshop - for a 1x1 pixel line and spacing:
create new document of 1x2 (W,H)pixels, RBG, 72 p/i, transparent background.
Zoom in 1600%, sqaure marquee a 1x1 pixel box, fill the selection with black.
Select all, then "Edit > Define Pattern".
Open the image you want, select the area you want the "TV line" effect (or select all) and then "Edit > Fill..."
In the Fill dialog, "Use: Pattern", "Opacity :20%", rest are default, unless other effects desired.
And thats done for photoshop.
2) Fireworks - TV line effect, this is the easy.
Create new document 1x2 pixels,
draw a line 1 pixel basic hardedge stroke.
make sure it sort of fills the top pixel of the 2 pixel height.
save the file in your Fireworks : Settings : Textures directory.
Open your document, draw a shape, fill it with the 1x1 pixel texture about 30%, set the object opacity to about 30% also.
There ya go, TV line effect.
As for other graphic programs (Paintshop pro), I not so sure, don't use them.
Maybe some one else can help.
Well it's easy if you have PSP 6. First start with your image open. Click on image on the upper menu. Then go into effects. Then you just find where it says blinds an click there. Once you do that just take the width down to 1. Then play with the opacity till you like what you see,