To marathon or not to marathon?

That is the question?  I am mentally committed to running the Madison half marathon on Memorial Day weekend.  And I had thought that I was mentally committed to the Fox Cities half in September.  But the more I think about it, the more I want to accomplish a marathon.  There are 15 weeks between the two races and I have looked at some of the training plans and I think I could do it.  Finding the time to do 13, 15, 18 mile training runs would certainly be a challenge.  Especially if (when) I get a job.  Can I really double my current weekly mileage...and then some? 

I'm not sure if I should wait to make the decision until after the half marathon in May, or if I should actually sign up for the Fox Cities Marathon and then be committed to actually training for it.  I will certainly be thinking a lot about this.  I hate not knowing what I should do.  I think what I really need, is for someone to tell me that I can't run a marathon, then I will definitely do it!!