What have I gotten myself into?

Ok, so Rachel over at Yarnagogo had this great idea to get us knitters off our tushies (or tusies as my daughter calls it) and get us running - or walking, or Nordic Tracking (great for my knees) - 100 miles by April 1. ONE HUNDRED. Not 10, not 50, 100. And what did I do? I joined up! I joined up the other day, and STILL HAVEN'T WALKED A MILE. I think I had better get my arse in gear, no? I can't run, my knees are too crappy. I can walk, and I have a course mapped out (Rach is right, Google's Pedometer is AWESOME! So now I know how far I have to go around my neighborhood to do a mile. It's doable, totally, I just haven't actually done it yet. I'm the queen of lame-ass excuses, basically. Throw off the idea I have in my head of what I need to do or how I want to do it, and I will promptly cut the thing I want to do least. I was totally planning on starting with 1 mile 7 days a week (walking outside, since my Nordic Track computer is on the blink, and I have no way of knowing how far I've gone on it), since that allows my knees to ease into it, and I figured that would allow some wiggle room if I have to miss a day. But I don't feel too optimistic about it so far, since I have already put it off about 3 days. Someone kick my butt, please? Please?