How to put duct tape into orbit for a dollar a day.

Step 1: Build Your Launcher

The launcher is made out of PVC. I used what I had around. It has 2 parts: an air tank, and a launch pipe.
The air tank is used because most valve stems don't let a large volume of air through at a time. The valve stem let the air in, but not out (duh!). The first time I made this, I cut apart i bike inner tube for the stem, drilled a hole in the end cap, and hot melt glued it together. That lasted all of 10 launches. Then I found car tire valve stems at the local hardware store, so use those. Just follow the instructions on the package to drill the right size hole.
The launch pipe carries the air from the air tank into the rocket. Mine is way longer than it needed to be, but then again, I planed on make some much bigger rockets latter :) (don't, unless you have somewhere far from any cars that can be damaged. the big one I made with a Nerf ball nose but a big dent I the neighbor's car, luckily he was a good sport.) It does help you not have your ear next to the end of the pipe, and thats very good considering how loud this is. The launch pipe is 1/2" water pipe. The rockets should fit snug on it, and are fed completely onto it before launch.
I later added a threaded fitting below the valve so I could take the launcher apart for storage. If you do, use Teflon tape so that it doesn't leak.

Step 2: Make a Rocket Tube

You will need:
Scissors
card stock of paper
Duct Tape
a piece of pipe the same diameter as you launch pipe.

roll the card stock on the pipe as tight as you can.
You can glue the edges of the card stock to itself if you want, but I don't. The rocket don't survive to many landings anyway, so why waste the time. Plus they are cheap to replace, and I can make one in less than a minute. Don't glue the paper to the pipe.
When you have it rolled, use a small piece of DT to hold it tight. If you can get some else to help, it is easier to keep it tight.
After that, cover the whole tube, but not the pipe, with a couple of layers of DT.

Step 3: Make a Nose Cone (sorta)

Slide the rocket tube to one end of your pipe. Slide it an inch or two (2-5 cm) past the end of the pipe.
Crimp the end flat, and fold a piece of DT over it. the reinforce the crap out of it. It will almost always land nose first, and some of these hit fast enough to spat flat when they hit. extra DT here is always worth it. Plus, extra weight at the nose help it to go higher.

Step 4: Make Some Nifty DT Fins

To make the fins, tear off a piece of DT about half the length of your rocket.
Fold it in half lengthwise, but don't let the outside edges touch. Push those edges against the bottom of the rocket. It will take practice, but once your get your own trick to it, they go a lot easier.
don't worry if it isn't perfect, as the fins don't make that much of a difference on the smaller rockets.
Trim your fins to shape, whatever you think looks good.
note: I drew some lines on the pipe to help me space my fins out.

Step 5: Launch That Puppy

To launch, simply close the quarter turn valve, fill the air tank with compressed air, put your rocket on, open the valve and, POW! there goes the rocket.
I use an air compressor to fill the air tank, but a bike pump would work. Slowly.
With the smaller rockets, it doesn't help to put more than 80 psi in the air tank. And at 60 psi, you get 90% of the hight.
Some thing to note:
Don't stand over the rocket when air is in the tank. These thing move. this is similar to a spud gun, and it will hurt to get hit at point blank. Bad.
It is loud. Keep your head away from the end of the launch pipe. It may piss off you neighbors. Don't blame me.
DO NOT try and catch a rocket on the way down. They are going almost as fast as they went up. It stings if you do catch it, and you really don't want to catch one on the head.

In spite of those warning, the small ones really aren't that dangerous, and won't damage anything. I make them with my Webelos, and so far the only harm happened when one of them tried to catch "The Big One" I made out of a full sheet of poster board, a Nerf ball and some coroplast (Corrugated plastic, like cardboard but made from sheet plastic. Think political lawn signs). And all the happened to him was a scrape from the coroplast.
They will bounce when they hit the ground.