Ali, I hadn't thought about the heat-n-bond - that's a good idea. Here's what I did:
- Buy shirt/sweatshirt/whatever
- Go to a fabric store and pick out either a pattern and a solid, or two solid colors. You don't need very much of the materials.
- Wash everything (important in case the shirt shrinks and the material doesn't, or vice versa)
- Cut your letters out of the print. Then pin them onto the solid, and cut around them leaving a small border. (phi's are a pain to cut!

)
- Take the whole thing and pin them onto your shirt, and sew 'em on. With 3 letters, like Ali said, it's easiest to place the middle letter first, then do the others.
It is sooo much cheaper than ordering letters from a store!! But be careful, you will have your sisters asking you to make letters for them