What are the strands of white diamond shaped streams tied around trees (usually around temples in japan)?

Question:

http://ih0.redbubble.net/work.7210724.1.flat,550x550,075,f.shimenawa.jpg

I've seen these and I don't know what they are or what they mean. I've also seem animes where priestesses have a stick with one of these on the end and they swish it back and forth. What does it mean?

Answer:

The zigzag papers are shide
The rope is a shimenawa
The stick with the shide is called a onusa
They are used to bless or purify evil in Shinto religion