Working out while injured..need help

Hello all,
I have been hitting Jillian Michaels, Banish Fat Boost Metbolism hard, and now my lower back is sprained (I think).
It hurst when I bend over, sit down and stand up. I do not want to use that as an excuse to stop working out. Just wanted to know, What exercises I can do, with an injured back? Thanks for you help.