I'm not a cyclocross rider, although it's something I want to try. I used to race mountain bikes, and because I couldn't just power over alot of the obstacles, I ended up getting off and climbing/running with my bike (a HEAVY 80s mtb!)
The best advice that I can give you, which may not be very good advice, is to ride, ride, ride. And run. And ride-and-run. Ride in the mud, ride in the cold. Upper body strength is essential, so you'll probably want to incorporate some weights and definitely core work.
There are some cyclocross clubs in some places (Baltimore has a big one). Ride with them or mountain bikers. Enter a race if you want, and see what your strengths and weaknesses are.
Perhaps next year will by my Cyclocross year!