Boot in Windows, insert the Ubuntu CD and wait for the Auto Start window (if Autostart is disabled, go to Computer and double-click the CD/DVD drive.)
Choose Install Inside Windows.
In the next window choose the Drive where you want Ubuntu installed, Language, the size of the installation (how much space should ubuntu use from the specified hard disk), wirte down Username (all in lower case) and Password.
Now click Install
And your job is done here, the next few steps are automated and Ubuntu does them itself.
After it creates image of the files, the CD eject itself and a window appears which asks to reboot.
Click Finish.
The machine will boot up and Windows Boot Manager will ask which OS you want to boot in, choose Ubuntu.
Your computer will start in Ubuntu after it takes a couple of minutes to actually install the files and after another restart you can start working in Ubuntu.
That’s it! Just like installing a program. If you want to uninstall Ubuntu go to Programs and Features or to the folder Ubuntu in the drive where ubuntu is installed and click uninstall.
Note: You can access windows files on the hard disk where you installed Ubuntu in Filesystem>host.
For a regular dual boot installation read How To Dual Boot Vista and Gutsy Gibbon