Some of the best times I had on skis last season were in the halfpipe. When you're riding it smoothly, your airtime can be a magical experience in weightlessness. Once you get the feeling, you'll be boosting huge airs over the lip in no time.
If the pipe is busy, there will usually be a line on either wall at the top. Wait your turn and yell "dropping next" before you go. Proper pipe etiquette is important.
After dropping in, really work to hold your line across the pipe (this will help you climb steeply up the wall and also give you more hits). Beginner pipe riders often take a line that is too straight down the pipe.
Keep your body perpendicular to the wall as you climb it; don't let the steepness intimidate you. When you get to the lip, "pop" or jump up (not out) into the air. The amount of pop varies with the shape and slope of the wall -- lots of pop on a flatter wall, just a little on a steep wall. The lip of a halfpipe varies throughout, and you must fine-tune your pop to maintain a smooth ride.
As you launch into the air, keep your knees bent. This gives you the option of either extending or retracting your legs for a smooth touchdown. Also, when you take off, you need to set just a small amount of rotation down the pipe, similar to an airplane turn. Try to land as high as possible on the wall so that you can get maximum speed for your jump on the opposite side.
If all of this still seems a little over-the-top, try to find a sidehill run at your local ski area. There will often be small re-entry-style jumps on the high side of the run where you can practice airplane turns and hone your skills.
Intimidation is the biggest thing holding skiers back in the halfpipe. It's not uncommon at my home area, Whistler, to have over 200 snowboarders in the pipe by midday, and I'm sure the situation is similar at other resorts. So head into the pipe early in the morning or late in the afternoon for your first few times. Once you see how easy it is to make it smoothly through the pipe, most of your anxiety should disappear. Halfpipe riding is more of a feeling than anything else, and the only way to learn is to get in there and try it.