O.k., Hardtail. Yes, get a new shock, it'll be a significant upgrade to what you have now. Like I said, stick to 80mm of travel for best performance. I'd suggest getting one of the new forks with adjustable travel, like the Manitou Black or the Rock Shox Duke or Psylo. That way, when cruising some singletrack, you can set it at 80mm, then when you want to hit some fast downhill or really rocky sections, you can bump it up to 100mm.
L8R
__________________
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW, What a Ride!" - unknown
"Your Bike Sucks" - Sky Yaeger