http://the-tech.mit.edu/KPT/KPT.html
If you use Adobe's Photoshop then you owe it to yourself to check out Kai Krause's page. Here there are 23 in-depth articles showing how to take full advantage of the tools provided with Photoshop and by Kai's company, HSC. You can also venture into an archive of image tiles that can be used as backgrounds for Web pages, or you can find more information from this graphics expert.