You'll have about two months to get ready. If you make sure to do a little biking and swimming while doing your running training, you shouldn't have a problem at all. Even if it's just two swims and two bikes a week, you can ramp up the training after the marathon and be in pretty solid shape by April. A buddy of mine ran a marathon the week before collegiate nationals this year. Granted, he went a little slow, but he didn't get hurt and didn't go that slow....maybe 2:20-ish? And he probably had 2:15 legs at the time. I think you'll be fine :)

It depends on your base and your fitness level. Assuming it's your first marathon-distance running event, I would advise against it. Even if you don't hurt yourself, the post-marathon recovery time is wasted tri training time. Insteading of hitting it hard 45 days before your A race you'll be icing your quads.

Thanks for the input guys, and keep it coming, so I guess my next question is will it help me go any faster? I don't really have a desire to do a marathon just to do one, the purpose is to give me a specific goal while I increase my running ability. The way I look at it, right now I'm racing like a little souped up 4-cylinder tuner. Running the marathon would be like trading that in for a small block V8. The actual marathon isn't really going to push my top end speed up that much, but in the build and peak phases it will let me put in a lot more speed. Hope that isn't a terrible analogy.

I assumed that you really wanted to do the marathon. If being fast at an oly tri is your goal, you will benefit a lot more from tri training. For example, my marathon-the-week-before-nationals friend and I were about the same speed a year ago (maybe 2:20-ish). After a couple months of marathon training he was down to about 2:15. After a couple months of tri training I was down to about 2:05. Marathon training will not give you a small block V8, more like the 4-banger tuner with some ricey exhaust tips.

Bump.

I have a sprint tri scheduled two weeks after a marathon. Serious training for both begins next week. I have been running since November, did a 1/2 mary in January. Jalyon, sounds like we are doing almost the same thing, any tips?

There is no benefit to running an early season marathon for IM training. So, I'm guessing there's no benefit for anything else as well... except for maybe an ultra.

If you look at most marathon training plans, they won't have you running more than 2.5 - 3.0 hours on the longest days. The idea is that anything outside of that has little return for the amount of recovery and potential injury.

If your goal is to run a marathon, then by all means, feel free to do it. But if your goal is a triathlon, limit your running races to half marathons and throw a late season marathon in to finish off the season.