I've had stress fractures a few times & Plantar Fasciitis (
http://en.wikipedia.org/wiki/Plantar_fasciitis) once. So my general dr., the podiatrist & the trainer I met with to get the basic layout of the gym have all agreed that I should wait until I'm 180 to start jogging. I'm still working on it (lower impact exercise like ellipticals, walking, etc. in the meantime).
I certainly don't want to discourage anyone from a higher intensity exercise. And anyone of any size can be prone to injury if they dive into a new exercise program too quickly. But those of us in the 100 or more to lose category are probably even more vulnerable, because of the weight put on bones, joints, etc. I'd start slow and/or run it by a dr.
One of my stress fractures happened because I started jogging without preparing my body properly for it. I had to wear a soft shoe cast for about a month and then my activity was still limited for a bit after that. I lost the motivation to exercise & gained even more weight. And eventually, I wound up at my all time high of 250. I'd hate to see anyone else have that kind of setback. Please be mindful of avoiding injury.