I thoroughly recommend Linux Mint 7 Main Edition which is built upon Ubuntu 9.04 Its easy to install and easy to use plus it comes with much of the software you are likely to need preinstalled
Linux Mint 7 Download
http://www.linuxmint.com/edition.php?id=38
Linux Mint 7 User Guide
http://www.scribd.com/doc/15884753/Linux-Mint-7-Gloria-User-Guide
The Perfect Desktop - Linux Mint 7 (Gloria)
http://www.howtoforge.com/the-perfect-desktop-linux-mint-7-gloria
You download the ISO. image of Linux Mint 7 then you need to create a Bootable LiveCD for installation
Linux Mint 7 can also be run direct from the LiveCD from Booting up without touching your Hard Drive
INSTALL LINUX WITHIN WINDOWS
Linux Mint has a feature called mint4win based on the Wubi installer (Ubuntu) http://wubi-installer.org/ which enables you to install Linux Mint within windows (Windows 7 run mint4win in vista compatability mode)
You keep Windows as it is, mint4win only adds an extra option to boot into Linux Mint. mint4win does not require you to modify the partitions of your PC, or to use a different bootloader, and does not install special drivers. It works just like any other application.
mint4win like Wubi keeps most of the files in one folder, and if you do not like it, you can simply uninstall it as any other application.
Boot in to windows insert the LiveCD you have just created and you will offered the option of installing inside windows which is where mint4win comes in, you will be asked how many gigabytes you wish to allocate to Linux Mint (I recommend 8gb) then you set a password for your installation then click install and thats it.
Once Linux Mint is fully installed upon starting your PC you will be given a choice of which operating system you want to use Windows or Linux Mint.
CURRENT SESSION
Linux Mint 6 ext3 with switchable Compiz 0.7.8 and Beryl 0.2.1*
http://www.linuxmint.com/edition.php?id=31
http://en.wikipedia.org/wiki/Beryl_%28window_manager%29
http://en.wikipedia.org/wiki/Compiz
*Beryl 0.2.1 sourced from Ubuntu 7.04 repositories
LUg.