1. Download Raspbian “wheezy” from the download page. This is Debian next version after Squeeze, optimized for the Raspberry Pi hardware so up to 40% faster.
2. Extract the image file 2012-07-15-wheezy-raspbian.img from the .zip file downloaded in step 1.
3. Insert the SD card into the SD card reader on your laptop and check what drive letter it was assigned. You can easily see the drive letter (for example G:) by looking in the left column of Windows Explorer. If the card is not new, you should format it.
4. Download the Win32DiskImager utility from https://launchpad.net/win32-image-writer
. The download links are on the right hand side of the page, you want the binary zip.
5. Extract the executable file from the Win32DiskImager zip file and run the Win32DiskImager utility. You may need to run the utility as Administrator.
6. Select the 2012-07-15-wheezy-raspbian.img image file you extracted earlier.
7. Select the drive letter of the SD card in the device box. Be careful to select the correct drive; if you get the wrong one you can destroy your computer's hard disk!
8. Click Write and wait for the write to complete.
9. Exit the imager and eject the SD card.
10. Insert the card in the Raspberry Pi, power it on, and it should boot up.
Note that these instructions are just a minor update to http://elinux.org/RPi_Easy_SD_Card_Setup