Nice to have you.

You might try posting in the regional forums (scroll down to the bottom of the front page and you'll find 'em) and see if there's anyone in your area who's looking for a ride buddy or knows of any good groups to ride with or good beginner-intermediate trails in your area.

I guess my advice about making your first forays into mtbing fun rather than miserable is to only take yourself a little out of your comfort zone at a time: something that scares you a little is way fun once you've completed it successfully, but something that scares a lot is, well, scary! If you think something's going to be tricky, ask someone to show you so you can take a look at how they do it and then practice that section a few times until you're feeling more comfortable - the practice will pay off the next time you come to a tricky bit. It can be pretty motivating to have a particular trail you ride regularly or semi-regularly, especially when you're starting out, because it gives you a good way to gauge progress and it's way kewl when you nail that really tough bit for the first time.

As for the crosstraining? I aways reckon you should do something you enjoy. I don't doubt that a good spin class has some great training benefits, but if you'd rather swim or run or whatever, then do that - you'll still be getting the cardio workout.

Hope that was vaguely helpful. Believe me, you can ask anything in these forums and someone will have a suggestion for ya.

Happy riding!

P.S. One last thing, you might like to take a look at the "Getting to know you" thread at the top of the "Open" forum. You can get to know us all a bit better, and you can tell us a bit more about yourself too, if you like.