I was big into mountain biking back in high school (at least I though I was at the time!) but then I sold out to the road/fixed gear world. I would now like to get back into mountain biking. I still have my old Giant Iguana and I would like to spend some time this winter upgrading it for the spring. New tires will be one of the first upgrades, but I also remember never being happy with the saddle and the bar/stem setup. How do I go about upgrading these items on the cheap? I don't really know enough to know what I want. I just want to try something new. Is used gear the way to go? Any advice that will get me back in the dirt again would be much appreciated.

Thanks!
Tom