First congrats on your decision! Babies are wonderful and being a Mom is so much fun!
I personally could not exercise at all as per my doctor (but yes every now and then I would pull out the extremely boring Kathy Smith preggo tapes) just to get some kind of exercise. I went from being a very active aerobics/spinning teacher to doing nothing so it was a hard adjustment. The only reason I could not was due to being high risk with a great deal of 1st trimester bleeding. Now, BF on the other hand taught spinning all the way up to 2 days before she delievered. It's just going to depend on your body and your doctor.
Always talk with your doctor about the do's and don't's and listen to your body.
Good luck to you!
Jana