Yes now you can run Ubuntu within Microsoft Windows with the help of this Portable Ubuntu package, its just like as if you are running Ubuntu system as a windows application. All Ubuntu apps will be available for access through a toolbar on Windows desktop, you will be able to exchange files and copy paste text from Ubuntu to Windows and viceversa. You can keep Ubuntu in your flash/usb druve and can use it anywhere you want. The main advantage is that you will be able to switch to anyof the operating system depending upon the app compatibility without the headache of installing new operating system on your machine.
Here are some screenshots
You can use Mozilla Firefox from Ubuntu toolbar
You can also use the Ubuntu terminal
Of course, it's also possible to install applications using the Synaptic Package Manager (for example, Amarok)
After the installation, you can start Amarok:
The password for the pubuntu user is 123456. It is useful know it when you need to use sudo or gksu applications (Administrative/System tools).
Instructions To Run Ubuntu in Vista [PDF : 3 Pages with screenshots]
Click Here To Download Portable Ubuntu