How to Install Windows OS if Already have Ubuntu 12.04 Installed

I have purchased a dell labtop with Ubuntu Linux 12.04 installed in it, and I want to install Windows Operating System on Ubuntu and have dual booting, Means to install the Windows OS in the another drive Except those drive where ubuntu has already installed. For Example - if we have ubuntu operating system in the C drive, then i want to install Windows Operating System In D drive. I don't want to uninstall Ubuntu.