Wubi 8.1 is Ubuntu Installer for Windows.  Wubi 8.1 helps you install Ubuntu OS on windows and give you Linux with just a Username and Password. The installation is fast, doesn’t require a CD, or patting your drives and such procedures. It is just like another application that can be installed when required. After rebooting it will show you an option for Ubuntu.
What is new with Wubi 8.1 is that it is compatible with Ubuntu 8.10, has Mythbuntu Frontend and is released after fixes minor errors detected in the earlier versions. This is one of the easiest ways of getting on to Linux, however it has no option of help and it requires the users to understand the working of Linux.