Agree that walk/XT refers to NOT running, but walking or cycling/swimming/elliptical. When I started running I could not have run 10 minutes without stopping as in the first week of the plan.
I would have exploded on the track and it wouldn't have been pretty. I started out jogging the straight sides of a track and walking the curves. That was more like 4 minutes of slow slow jogging and then 3 minutes recovery. I built from there, trying to run a little farther each week.
I agree with MBN on 2 points. Slow is FINE. Better to go slow and keep going for a few minutes than to try to bust it out and kill yourself in 30 seconds. You do NOT have to be a speed demon, ever really, but especially not when you are starting.
Also the SHOES. Absolutely get fitted for good shoes. Worth every penny. Go somewhere they will watch your stride. Brands and styles vary greatly and you need one that fits your feet and your stride to avoid injury.
I agree with her stretching advice too.