Flashing an SD Card using Windows (XP or 7):
The most popular and stable standalone distribution at the moment is
Raspbian Wheezy (Debian) Raspbian Jessie – this will give you a bit more control over installation , you can download all the software here. You will also need to format the SD card using SD Formatter, install this to your PC and launch the software; select the correct SD Card from Drive Menu and click Format – leave the option to Quick Format unless you have an old SD Card that has been rewritten a lot.
Having downloaded your OS of choice, you then need to download WinDiskImager from here ; unzip and install it on your workstation (I assume you know how to download and install software on a PC). Open up the Win32 Disk Imager, identify and select your downloaded image file (ex; 2012-12-16-wheezy-raspbian.img) and ensure you have selected the correct SD Card in Device Window: you should see something like this:
Select Write – this will take up to 20min depending on speed of PC/Processor, time for a cup of coffee and a donut. When finished press exit , eject your card before removing it and you’re ready to start your Raspberry Pi.
UPDATE; Go here for the EASY Raspbian OS install procedure.