open in Photoshop, convert to grayscale (Image/Mode/grayscale) then to Bitmap (Image/Mode/Bitmap). In the dialog box that comes up, leave your input resolution alone, up the output resolution to 1200 (this makes better dots, even from a low res image, but you can't really enlarge the image) Under "Method" set it for Halftone screen, they set your line count and angle. I couldn't get the file to upload, so here's a link to my Photobucket page
You can see the difference the higher output resolution makes on the final image...
Steve