Using P90x and Overweight?

I am around, what I consider, 40 lbs. overweight. All the people I see on the P90X infomercial look fairly in shape. But is this a good plan for people wanting to lose a lot of poundage? Or do I need to lose some more weight before starting this up? My activity level is sitting at a desk for 9 hours a day. But I still am young so I really don't have any joint issues and I heard those were used alot