Hey Frank, If you know photoshop or any pixel based design software its easy. The only thing different is the output. Where you would normally just send to a printer or publish to the web. You now have to separate the colors for screenprinting. The only things to keep in mind from a design standpoint are Resolution and Dot gain issues. I have worked in several shops and I have found that most screenprinters work in mid-res. where hi-res would be 300dpi or higher at actual print size like for standard magazine prints and low-res being 72dpi for web use. My personal preference is 220dpi at actual print size. I have found that to be a good balance between print quality and optimizing rendering speed and effects settings on my filters and plugins. The other is dot gain. For the most part if you can design it you can print it. However I find that some effects that look great on a backlit monitor don't translate so well to the relatively low res printing we do in screenprinting. This is not to say you can't create eye poping graphics for screenprinting. You obviously can. It's just that some subtle gradients and photorealistic effects are hard to reproduce even with high mesh count screens especially on dark shirts. I suggest a training dvd or a book like "photoshop for screen printers" by Joli Ballew.