Hello!(unresponsive overweight dog )

Hello, new to the site today, looking for help with my neurotic beagle. Newly adopted (july of 2010) she is 8 years old and per her SPCA vet record: "morbidly obese" but she is calm, and mellow, and that is what my kids wanted. (they are intimidated by large and very energetic dogs)... she is down 5 lbs since we got her, but seems to be 100% fully motivated by food alone, and wants nothing to do with us unless we are eating. wont play, refuses to go on walks, sight of leash actually makes her cower. got her to walk excitedly, while holding treats... then she was down for several days with backache (vet treated) dont want to be obsessive, but do want her to get healthy.. help!