Installing Ubuntu as a dual-boot with Windows without partitioning
http://www.psychocats.net/ubuntu/wubi
You keep Windows as it is, Wubi only adds an extra option to boot into Ubuntu. Wubi 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.
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 Ubuntu 10.04 LiveCD and you will offered the option of installing inside windows which is where the Wubi installer comes in, you will be asked how many gigabytes you wish to allocate to Ubuntu (I recommend 8gb) then you set a password for your installation then click install and thats it.
Once Ubuntu is fully installed upon starting your PC you will be given a choice of which operating system you want to use Windows or Ubuntu
Ubuntu 10.04 Download
http://www.ubuntu.com/desktop/get-ubuntu/download
Ubuntu 10.04 (Lucid Lynx) User Guide
http://ubuntuguide.org/wiki/Ubuntu:Lucid
If you do have a CD Drive Linux Mint 9 which is built upon Ubuntu 10.04 has a similar feature called mint4win and the directions given above for Wubi can be followed
http://duncsweb.com/2009/09/27/mint4win-a-wubi-based-installer-of-linux-mint/
Linux Mint 9 Download
http://www.linuxmint.com/edition.php?id=52
Linux Mint 9 User Guide Download pdf.
http://www.linuxmint.com/rel_isadora.php
Ubuntu 10.04 and Linux Mint 9 can also be run straight from the LiveCD without touching your Hard drive
LUg.