To lose weight, sprint. To gain mass in your chest, bench press. To gain mass in your abdominals, do weighted crunches. Doing 20+ crunches is useless and pretty mindless. You DO NOT gain muscle nor strength doing 20+ crunches. Add weight until you can do 8-10 crunches. Do 3 sets, 1 time per day, 3 times a week. To gain mass in your arms, do 8-10 reps, 5 sets of dips and chin-ups, adding weight if you can do more. If you think hard enough you'll be able to find things around the house to do them on, rather than spending money on a machine. Also, I strongly recommend that you squat and dead-lift. And a healthy diet, of course. :)