Here is a simple and easy way to write an OS onto an SD card for your Raspberry Pi…
Raspberry Pi downloads: http://www.raspberrypi.org/downloads
MD5 and SHA-1 check sum utility: http://download.cnet.com/MD5-SHA-1-Checksum-Utility/3000-2092_4-10911445.html
Win32 disk imager: http://www.softpedia.com/get/CD-DVD-Tools/Data-CD-DVD-Burning/Win32-Disk-Imager.shtml
The Raspberry Pi Guy
The Raspberry Pi is a credit-card sized computer that plugs into your TV and a keyboard. It’s a capable little PC which can be used for many of the things that your desktop PC does, like spreadsheets, word-processing and games. It also plays high-definition video. We want to see it being used by kids all over the world to learn programming.