I thoroughly recommend Linux Mint 10 Main Edition which is built upon Ubuntu 10.10 Its easy to install and easy to use plus it comes with much of the software you are likely to need preinstalled
Installing Linux as a dual-boot with Windows without partitioning
http://psychocats.net/ubuntu/wubi
Linux Mint has a similar installer called mint4win (mint4win works the same as Wubi so the instructions outlined above are almost identical)
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 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 Linux Mint LiveCD and you will offered the option of installing inside windows which is where the mint4win installer 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
Linux Mint 10 Download
http://www.linuxmint.com/edition.php?id=67
Linux Mint 10 User Guide
http://linuxmint.com/rel_julia.php
You download the ISO. image of Linux Mint 10 then you need to create a Bootable LiveCD for installation
https://help.ubuntu.com/community/BurningIsoHowto
Linux Mint 10 can also be run direct from the LiveCD from Boot without touching your Hard Drive
LUg.