You can so do this.
I started running June 24 2012. I am a outofshape overweight 50 yr old bad asthmatic who just completed her first Tinker Bell.
I did the Galloway and ran/walk/ran the race and finished in an upright position. I never saw the Balloon ladies or the sweepers and did not have one bit of trouble with my asthma during the race.
I dropped 20 pounds and increased my lung function so much in the 7 months from the start of my training to race day and my doctors are smiling bigger than me at my accomplishment. I had Jeff Galloway as a online trainer and he worked out a program for me that took my asthma and lower level of fitness into consideration and because of him I DID IT.
Start out just walking, walk to the end of the road, then walk to the next block, progress to that mile. Then add in a few jogging steps, then do the couch to 5k. Enter a few 5k races that are friendly to walkers. Complete one at a fast walk, then you will want to walk/run one. Then look out Tinker Bell.