The idea from this came from tv. I saw teh pre-made kit that does basically the same thing i did but I am sure that it costs a little more than what i spent, although the extra time I spent could have easily been accounted for in cash... it takes about 6 times longer to install but at least you dont have to go get it or find it or pay for it.
If you already have plastic wrap and masking tape.
Step 1: Get all Materials together
Wall-friendly tape- anything that dosent leave marks and is removable
Plastic Wrap - uh, any kind of plastic i think..
Electrical Tape - for parts where flexible tape is needed
Step 2: Line up the Roll
You can start at either end, and leave about 4 inches off the side of the window, enough to let it touch the wall and you can tape it easily.
Each pass should cover the previous one by at least 2 inches i did it like 4 inches.
Also pay attention to how many you are going to need to make across so that you can space them accordingly.
Step 3: Tape end of roll
nothing has to be exact, but put half of the plastic on the tape and leave the other half of the tape exposed for the next step.
Step 4: Re-inforce tape with another tape
this was enough for me to make sure that it didnt fall off, even when i tugged on it a little bit.
If your carpet is dirty or just hard to see the plastic you can put a piece of paper underneath and it might be easier.
Step 5: Put it on the wall
you know, stick the tape on the ceiling.
Make sure that you put it on straight and there should be no messed up edges on the plastic, if there are, spend some time to fix them.
Step 6: Cut
you can leave it dangling, and make your tape for the bottom if you have to.
Step 7: For bottom tapers
just make another tape thing for the bottom, it should be able to work but if it does not use pushpins to hold it on there