Glashopper, I understand what your sayin' and stuff. Most people with asthma think they can't run long distances. The majority of our Cross Country runners have asthma, if not that poor joints(I'm in that group).
Anyway, try practicing breathing from your diaphram.(Sorry more band methods) I just switched to Tuba and that sucker takes alot of air. If you breath from your diaphram it will flatten and it gives a place for your lungs to expand rather than trying to move your rib cage.
You might also try running, biking, or swimming a bit if your lookin' for endurance stuff and it's a great way to lose weight. If you choosing running, I think even running just a mile a day would help you a lot. You may think a mile is alot but it's really not.
Hope this helps! Try playin' a tuba sometime! :-D Good luck!
-Lothmir (Flower Jewel)