Linux comes in different versions (called distributions, or distros for short).
Different people have different opinions about which is best, and some are suitable for newbies and some are more suited to experts.
My favourite is a very well known distro, well suited to beginners like yourself, called Ubuntu. http://www.ubuntu.com/
It comes with a wide range of applications and is very easy to use.
One of its strengths for people looking at making the switch from Windows is its Wubi installer:http://www.ubuntu.com/download/ubuntu/windows-installer
It is also possible to run it directly from CD or USB drive without making any changes to your computer. This is useful for evaluating it, and making sure all your hardware works correctly:
, scroll down to "Burn your CD or create a USB drive" and click on "Show me how"
Remember there are other distributions, Ubuntu is just my favourite.
Hope that's useful