Hi Chub,
A couple of months ago I started my running program when I was just under the weight you are at now. When I first started I thought I would die (or at the very least my heart and lungs would explode) but now I have to say that running is my passion.
When I first started I was keeping about a 4.5 mph pace and could only go about 4 tenths of a mile but now I am running at a 5.5 - 6.0 mph pace for up to 3.1 miles.
The way i did it was by doing interval runs. I would walk for 45 seconds or so and then jog for anywhere between 20 seconds to a minute. Each week I would increase my runs and decrease my walks and it wasn't long before I started to see the results in both stamina and distance.
Now I do at least a 2 mile run per week and most other days I incorporate intervals or incline work but I am continuing to build. My legs have gotten much stronger, my lungs have tons more capacity and that runner's high....well, I just can't say enough about that.
Stick with your program...don't over do it and you will see the results. Running is about the greatest thing I've ever tried and I can't believe it took me reaching the 40 year old mark to realize that.