I've been doing WW since Sept. 2003. I believe in Week 3 of WW, you will receive information on calculating activity points. There is an AP slider and AP are based on your weight, workout intensity (light, moderate, and high), and time spent.
I use a heart rate monitor which calculates my calories burned. The rule of thumb is 100 calories burned = 1 AP. I actually count 1 AP for every 75 calories burned since food points are generally between 50-75 calories. I usually burn around 400 calories for workouts like Boot Camp, Step Blast, Imax2 and give myself about 4-5 AP for those workouts. I weigh 151 lbs. Of course, calories burned are different for each person.
Hope this helps some... Good luck with WW. It's a great program. I've lost 65 lbs on it.
Michelle