Depending on your leg injury, you could get a turbo trainer to put your bike in for stationary training. Earlier this year I badly twisted my knee & there was no way I could run, but could cycle indoors without any problem. The other advantage of the trainer, is that you can cycle during the worst weather without fear of incident.

I use a Kurt Kinetic Fluid trainer & have had it 4-5 years, it's still as good as new. I think the fluid filled trainers are the best. Don't bother with cheap friction controlled units or you will choke on brake dust.

I also use Spinervals training dvds with the trainer, to get a focussed workout & prevent boredom.

Here's a link to Kurt Kinetic: http://www.kurtkinetic.com/road-machine-p-198-l-en.html

Swimming is a great idea of course, you may find aquarobics sessions available. Contact your pool to see if they allow the use of flotation belts, if they do, go for it.  Don't worry about any strange looks, they will just be jealous!

Well feeling really down at moment ,having been knocked of bike 3 weeks ago have grade 2 sprain left wrist,and I am left handed so this is a problem.also injured leg so unable to run for at least 8 weeks .

good job the marathon is not until next year so have time to do some good training ,going to go swimming seems to be the best way of maintaining some fitness.has anyone got the floatation belts for running in a pool.I have brought one but have not used it yet .want to know what they are like and do you get wierd looks in the pool.