Virtualization can be fairly complicated or very complicated, depending on what kind of Virtualization you are trying to do. What it is is running one operating system within another. A number of large companies are doing this with their servers where they have a basic operating system that is probably some version or "flavor" of Unix that is light weight on resources that other more powerful operating systems are loaded into as seperate entitites. So for instance instead of having a separate server for Windows 2008 that handles the corporate Sql database and a Windows 2003 Exchange server for their email needs, they have one server running a small core operating system (unix) that has two separate "virtual" servers (the 2008 and 2003 servers) running on top if it. It's goal is to allocate resources to the system that needs them the most at any point in time. The usual goal of virtualization is to centralize administrative tasks while improving scalability and work loads.
But, it can also be used for some other senarios. One thing it is very handy for is to move to the next level operating system. Windows 7 had been very popular and a number of people are moving to it to remain current with Microsoft. The biggest resistance to the change is what about all the stuff I've got installed in my Windows XP computer? Well it is possible to take an image of your Windows XP computer and "restore" it inside of a Windows 7 computer. So you can take your time learning Windows 7 and take a little time to install your most important software, but anything that you need is still available in your virtual XP. It is another icon on your Windows 7 desktop. You need that expensive voice activate software that does not want to install in Windows 7? Open up your Windows XP right on your desktop and it's available to use right now, not in 6 weeks when the manufacture gets around to updating their software.
* To the right is a Windows 7 system running Internet Explorer, Outlook 2003, notepad and paint. In the middle is the virtual XP running Windows Explorer, a video camera and showing the XP properties.