More than a marathon, but this is the closest topic I could find.

I've been running for three years(high school running) now and am thinking about running a 50 miler in the fall of '08. The main problem is that it's right at the beginning of indoor track and I don't want it to mess my training up. Do you guys think I could do it with the training I get from high school Xc and then be able to continue on into track?

People have run 50 mile races on very limited amounts of training. It all depends on whether you want to run it based on fitness and preparation, or based on heart and determination. I've run 50 mile races basically on marathon training and it was very painful, but finishing was never a problem. I've run 50 and 100 mile races on good training, and they were quite enjoyable. The core that I use to prepare for ultras is back to back 20 milers on consecutive days. How many marathons have you done?

running guy.

Glad to hear you are looking into ultra running, it's a great part of the running experience.

Most seasoned coaches would suggest you wait to run an ultra until you are in your late 20's, at the earliest.

High school and college runners are doing less distance these days, and err on the side of being under trained.
Too many injuries stop too many runners mid season.

Focus on XC, Indoor and Outdooor this coming year. A solid base of training over the summer should be your goal, as
you'll need it to get through the Fall season. Talk with your XC coach late track season and put a summer plan together.

Marathons and Ultras can be part of your running down the road. Have fun now while you have the speed for track and XC.
Go for the longer stuff once you have more years behind you.

Good luck!