Get off the Couch and Run 5k
http://www.mayoclinic.com/health/osteoporosis/ds00128/dsection=prevention (link to Mayo Clinic info on osteoporosis)
I found this really great guide to help me get started with my 5k goal online here:
It's called "From the couch to 5k in 9 weeks." It seems pretty good and I am determined to be running 5k before the end of the summer (with a long term goal of 10k by the end of the year). I had to modify this program a bit as I am using an indoor track that seems to be an odd length (270m). I know that it would probably be better to run outside but its cold and snowy here for most of the year (it snowed yesterday and its almost June!!). Running on a path will be more difficult that running on a track and running on a track will be more difficult than running on a treadmill (if you don't believe me, give it a try yourself).
I recommend using the guide above to get yourself started.
I am over half way through the program and I may be slow but I am pretty proud of myself. A side note here: you should be able to talk while running (maybe a bit breathy), if you can't talk you are running too fast for your fitness level. If you do run at the correct speed, you shouldn't get a side stitch (something that I didn't learn until recently).