I totally believe you can!
I have a good friend who went through boot camp for the Marine Corps last year. His attitude now is basically something's suck but you can do pretty much anything. He's in language school at the moment and woke up one morning to have his platoon leader announce they would be going on a 20 mile run before the end of the week. Oh and part of it was on the beach. Oh and at the end they had to run up the side of a mountain and then run back to base.
Now Marines are in good shape but not all of them are runners. They did have a couple injuries but for the most part the platoon came through just fine. Sore? Yes. Tired? Yeah. But alive and well for the most part.
I'm a big believer in the idea that we can do a LOT more than we think we can. Marines prove it every day, but so do a lot of normal folks.
One of the first things I thought of when I read your post was a blog, back in the early days of blogging, about two ladies who biked from Boston to California. They blogged nearly every day and uploaded the results as they had internet access. It's an amazing story. You can still go to the website and read the posts starting at day 1. They talk about their fears and excitement and you see all the ups and downs as they go. You can Google "Intrepid Bikers" or click this link
(I'm still not sure about the rule on links here so i'm assuming it might get deleted.)
Both of them kept separate journals. When I read it I'd read one for the day then flip to the other so I could see both of their thoughts/interpretations.
I think anyone can be motivated by their story but Randi I think in particular you will find it a great support as you train!