To install Raspbian on a Raspberry PI you need an SD card, at least 4GB and the image of the Raspbian OS.
Download the image from http://www.raspberrypi.org/downloads. The latest version of Raspbian is called “wheezy”: 2012-12-16-wheezy-raspbian.zip. Unzip file and the result is “2012-12-16-wheezy-raspbian.img”.
Write it to SD card using the UNIX tool dd. Windows users should use Win32DiskImager.
When done, insert SD card into your Raspberry PI (don’t forget to shut down PI before this operation).
Boot the RPI!
Username: pi Password: raspberry
Install Raspbian “wheezy” on Raspberry PI