Just thought I'd let everyone nice enough to reply know where I ended up. I purchased a Giant MTB about two weeks ago. Since then I've put 45 miles on it, including one great day on some single track and several smaller trips through the woods. The best part is no back problems. I'm doing crunches and the back bending stretches (also recommended to me by a physical therapist) to keep things loose, but so far so good.

Thanks for the input.
C.