Like SheFly mentioned earlier, sounds like you are pulling up on you handlebars, thus lifting you front tire off the ground. What if you find a not quite as steep of a hill and practice - shifting and standing. Typically when you stand to climb you will want to be in a harder gear than if you are sitting. If you have ever watched a video of something like the Tour De France you will see the riders change gears prior to standing up. Also as they stand you will see them position their weight more to the front of the bike. Do an experiment and as you are beginning to climbing and wanting to shift gears try standing up there, just to get used to the motion of standing without being on the steep part of the hill. You will get this hill conquered so don't give up!