Wubi: Install Ubuntu Inside of Microsoft Windows

If you want to try Ubuntu Linux but don't want to repartition your Windows hard disk, this might be the tool for you to consider...

Wubi - Ubuntu Installer for Windows

Here's the description on its website: 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 is spyware and malware free, and being open source, anyone can verify that.