I got my letters from Greek101.com. Go to the shirt configurator and put your letters in. Then copy the images to your computer. If you have something like Adobe Photodeluxe, use that to resize the letters to 4in (the average size) and then print them out. Just cut them out and now you have a template!
If you have trouble with that, PM me and I can get them for you and e-mail you the resized letters.