For your hands, you might want to try "bar-ends" on your mountain bike, if you don't already have them. These are inexpensive (about $15) extenders that go up on either side of your handlebar to allow for more positions as you ride. If you have "straight across" handlebars, you might be leaning forward too much and putting a lot of weight onto your wrists and hands. For me, the key has always been to vary my position as I ride.
For your butt, about the only thing that seemed to work for me in the past was just time in the saddle, and even with a lot of miles on, after 60-70 miles the pain crept in. "But" I've become a believer now in those split seat saddles. I just got a Serfas at my local neighborhood bike shop, and was astounded to find myself having NO butt pain during or after a century ride last week.
Hope you find things that work for you, biking shouldn't have to be painful! Good luck.