Sorry to hear about your injury, but don't be downhearted, you'll be riding before you know it.
I tore my ACL windsurfing in 1993, and the second guy i saw (Bert Zarins at MGH) thought that with a really good carbon-fiber brace i could do most anything i wanted to. he did say that eventually the joint would become too loose, and that then surgery was the way to go, but that surgical techniques were steadily improving, so that by the time i really needed the surgery it would be a better procedure.
I rode, windurfed, skiied, everything, for about 5 years, and then had reconstructive surgery, replacing the ACL with a hamstring. Rehab was damned uncomfortable, but I was on stage (I'm an actor) within 6 weeks and out sailing in about two months. The knee is now fully recovered.
Go with a surgeon who deals with athletes, and make sure you're comfortable with the diagnosis. Good luck