There is progressive muscle relaxation in the Resources. It is explained pretty well here...as well as a breathing video for panic...but my favorite breathing exercise is the divided breath, which I will post below.
Self Help sites with breathing/relaxation exercises instructions
Panic attack relief exercises:
http://www.healthyplace.com/
http://www.stress-relief-exercises.com/
http://www.ehow.com/video_4405003_breathing-exercises-panic-attacks.html
http://www.psybersquare.com/anxiety/panic_relax_I
The Divided Breath:
Imagine your lungs as having 3 parts. The bottom third, the middle, and top third. On the inhale fill the bottom third first, then the middle and finally the top third. Make sure that this is one continuous breath, but divided, with a slight pause in between each third. Hold the breath in for 3-5 seconds if possible. Exhale in reverse. First blow out the top third, then the middle, and finally the bottom third of your lungs until all air is expelled. (remember the pauses) Repeat several rounds for a toatal of about 10 minutes. Practicing this every day will not only give you control and structure to your breathing, it will strengthen and loosen the thoractic muscles, allowing better, more productive breathing, and relieving the chest tightness!
You will probably need to practice this several times a day for awhile until you can finish one round. I did and that is okay, it is hard to do at first, but keep trying, it will get easier and then begin to help.
I have to run for now, but will check in on you later .:)
S.C.