hi,
can you be a little more specific on "killing me"? would be easier to discuss if you can expand a little more on the biomechanics that go along with your pain...
what part of the ankle (front/back, inside/outside), hurts with what motion/type of kick, hurts when weight bearing on deck or only when finning, etc? also, anything make it feel better? (ie. stretch in a certain direction takes the edge off? better on first dive of day than last?)
my initial thoughts would go along with zippsy's line of thinking - probably the wrong fin for your type of kick, strength, size, or the like.
in general, treat scuba like any other sport. it's kinda like going back to the gym after a hiatus... easy to overdo it when you haven't done it in a while. i usually get in the pool for some regular finning a week or two before a big trip to get the legs used to it again. also, you might try a pre and post dive stretch, make a concious effort to break up the repetition (repetitive motion is a "killer" on the human body) and/or try alternating kicking types.
- lorien
(normal healthcare practitioner disclaimer applies... comments are for discussion puposes only and are not intended as professional advice)