That sucks! I am in the middle of my off season workouts too. Hope you get better quickly.
Not sure about the Achilles but for other types of injuries I've heard the acronym R.I.C.E, which means Rest, Ice, Compression, and Elevation. Stay off it, ice it every 20 minutes, keep it wrapped up with an ACE bandage or something like that, and try to keep it elevated as much as possible, preferably above the heart (lie on the floor and put your foot on a chair or something while icing). That mainly helps keep the swelling down. Not sure if that will help this type of injury, couldn't hurt the way I look at it.
Also, check this out:
http://www.webmd.com/hw/foot_problems/tr1811.asp
Has some good information on it. Good luck and let us know what happens!