From your description displaced into my ankle causing alot of internal damage to ligaments and tendons, I would say that intending to complete the half marathon in less than 3 weeks time, if you are still aiming for the one at the end of May 09, you are potentially putting at risk the no long term effects quoted by your surgeon.
In my experience of recovering from accidents (of which I have several) do not try to push your self to recover faster that your body is prepared to i.e. if something hurts or aches stop!. On the other hand most doctors I have spoken to are used to dealing with inactive people and they have always been suprised about how I have progressed over their expectations.
Well, despite having the best conditions I have run this in, not too icy, not too soft. I managed to achieve my slowest time ever, which I put down to still having the cold I picked up over christmas and the fact that I have not done any running at all since October.... hmm could be a factor do you think?
A great day for the race though, not cold and little wind. After the previous 3 weeks 'in the freezer' very enjoyable.