Follow the weight training plan outlined across the next pages. To supplement your weight workout, do at least 30 minutes of aerobic exercise–such as walking, cycling, or kickboxing–on alternate days.   To determine how much weight you should be lifting, choose an amount that is difficult to lift on your last repetition. General guidelines for women are 5 to 10 lb for light weight workouts, 10 to 15 for moderate workouts, and 15 to 20 for heavy workouts. (For men, 10 to 15, 15 to 20, and 20 to 25, respectively.)   If you’re new to weight lifting, start with a basic program: Do the light weight workout three times a week for 2 to 4 weeks, progressing from 1 to 3 sets of 12 to 14 reps each. Advance to the moderate weight workout, 1 to 3 sets of 8 to 10 reps each, for another 2 to 4 weeks. Then try the full routine: heavy weights workout on Monday, light weights workout on Wednesday, and moderate weights workout on Friday. You’ll melt away pounds without the crucial muscle loss that comes with aging.   Get this workout to go! Download it to your iPod, iPhone, or media player.