| Yes, diabetics have run long distance. Of course, we're all individuals with metabolic and treatment variance, so while I can give you general things to watch and look for, in the end you'll have to collect your own personal dataset and develop your own way of handling your needs.
I would caution you about concluding your episode of feeling weak and nauseated was low blood sugar, if you're basing that on feeling only. I've had high blood sugars which have resulted in me feeling weak so just going by feeling can be dangerous. Especially if you had been trying to go at it hard, generally speaking the higher you run the heart rate up towards the anaerobic threshhold, you might observe a tendency for blood sugars to go up as the body responds the stress and taps into the glycogen reserves to provide glucose for fuel.
The other more running-oriented concept I'd ask you to consider if you pursue a goal is to think of it as a long term idea and that some patience can go a long way to insuring that you achieve your goal with little discomfort and danger.
At the end of 2006, I broke my tibia inside of 7 weeks of running. I ran too hard too soon too much. While my leg healed in a cast for the first 6 weeks of 2007, I did my best to educate myself more about running along with the importance of diet and recovery for the legs. I decided I could get back to running and be able to do a half-marathon in 7 months time, but even that was a bit close I thought. Still, I carefully pursued a gradual buildup of miles and running and successfully completed a half-marathon on November 18th. It was one of the best experiences of my life to run 13.1 miles and it was a challenge.
A marathon isn't even simply twice the challenge of a half-marathon though. There are further issues that make marathons substantial undertakings for training commitment. I'd suggest that you consider thinking of working towards a marathon in a stepwise manner -- work on building yourself to being able to run about 30 minutes straight and see about entering a 5K race. Then see about building up to running for an hour and going for a 10K race. Then give yourself a year to do a half-marathon.
I did a half-marathon last November and I hope to do at least 2 more this year. But marathons aren't even on my radar yet. After I run my halves this year, I will consider how much progress I've made and see if I want to make 2009 a year to go after a marathon. If I'm not ready for that, then I'll run halves again in 2009.
Good luck. Collect good data. It can be done but it's not something that you just lightly do, it will take time and commitment and maybe some courage too. | 
