Lifehacker.com posted an article two days ago about how users can dual boot Windows 7 with either Windows Vista or XP.
They outlined two steps. The first is about partitioning the hard drive of the PC. The second is installing the Windows 7 operating system.
The process involves a burning tool software such as ImgBurn and a partitioning software such as GParted live CD.
Screen shots are included in the tutorial to make sure that those who want to attempt this process can easily follow the steps.
Source: Lifehacker.com

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Man, these LifeHacker guys are quick! I hope they’re making money off their blog!
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This article, Dual Boot Windows 7 And XP Easily: Windows 7 Installation Directly From XP Without A LiveDVD, shows you how to install Windows 7 directly from a previous version of Windows, without burn a DVD. The applications installed in the previous Windows version does not need to be reinstalled: they also work in Windows 7 , just create shortcuts.
You will be able to dual boot both operating systems and you will do not loose any data.