EDIT (April 23, 2007) : Finally got around to finishing the tutorial, which now includes not only creating the denim texture, but also the seams, wrinkles, and threads! I hope you'll be happy with the results. I'm really pleased with the way it turned out, if I do say so myself! The original tutorial has been deleted.
If you need the scanline pattern, you can download it here: [link]
This tutorial is in html format. Just download the zip file to a convenient location, like your desktop. Double-click the zip file and move the html file and the "Tutorial Images" folder to your desktop (the files folder and html file must be in the same location for the images to show up.) Double-click the html file and the tutorial will open.