How many pounds of chicken is needed for 100ppl

Hi Cher,
This is a very helpful site when cooking for crowds: http://www.dummies.com/how-to/content/cooking-for-crowds-for-dummies-cheat-sheet.html

I'd go with 110 pieces. of Leg and thigh cuts. Instead of weight.
And maybe a Lebanese/Greek style lemon chicken with the skin on for the recipe.
This would also give you a paring for a other Greek/middle eastern dishes. Humus...pita bread, Little 'kibbe/Kafta' type meat balls. Yogurt dip--tzatziki .
Tabbouleh (made with quinoa) and feta cheese on the side for the vegan veggie guests and does double bonus for glutin free folks---serve leafs of endive to make fingerfood friendly. With the feta on the side. And a bottle of good olive oil to drizel for extra flavor..and salt dishes.

It also depends on what else is being served and whether it's for a light lunch or hefty dinner.

Are you able to provide any additional info, like how it will be prepared and in what context it will be served?