Hey Tri girl - from another new mountain biker I would say the following:
1. Try to get out for a ride with an experienced mountain biker. It really makes a world of difference (Sadiekate was gracious enough to come out with me and its amazing how much I learned on one ride).

2. Get a copy of the DVD Performance Mountain Biking with Ned Overend (if you are like me techniques sink in a little better if I can see what people are talking about). Also its a great reference to have when you screw up on a ride and cant quite work out why.

Good luck and enjoy those trails.