I started mountain biking about 3 years ago... and since then I have gone through 3 bikes. If I were to rate myself, I would give myself an honest advanced intermediate/expert level rider.
What I've learned:
1) Go to a local bike shop. Talk to the people there. If they are working at a bike shop, chance are that salesperson/manager is a biking FREAK. Ask their opinion on bikes/gear. Give them your price range, they can get you into what you need. Yes, the internet is a great place to save $$, but IMO nothing can beat the support/advice you can get at a good LBS. Having a great local support network will assist you on not just the purchase, but also the after care that is needed.
2) Get the right size bike. You can do this by referencing #1 above. I started out on a small frame, but after experimenting and "demo" -ing different size frames, I found out that a medium size frame with medium length cranks is what I can spin most efficiently on, with the most control and comfort for my riding. I never would have figured this out without a great LBS to support my experimenting.
3) Buy the best bike possible within your budget. Like many other hobbies, IMO its best to go a little overkill to begin with to give yourself room to grow. I know, in this economy its asking a lot, but I could have saved myself a LOT of money since I started this sport if I spent a little more upfront. I'm not saying go out and drop $7 grand on a Specialized S works full carbon / full susp... but maybe consider buying a used bike at a great savings, which will put you on a more efficient machine.
With alllll that being said, the most important part is you get out and RIDE
Sorry I can't give advice on your actual question, but hopefully my post isn't 100% verbal diarrhea LOL