Perhaps the easiest way to run Microsoft Windows XP within Windows7 is through Windows XP Mode and Virtual PC. Windows XP Mode and Windows Virtual PC, available on Windows 7 Professional and Windows 7 Ultimate, allow you to run multiple Windows environments, such as Windows XP Mode, from your Windows 7 desktop. For those who do are not currently running Windows 7 Professional, Windows 7 Enterprise, or Windows 7 Ultimate, there is an easy upgrade path to Windows 7 Professional or Windows 7 Ultimate through the Windows Anytime Upgrade program.
Windows XP Mode works as both a virtual operating system as well as a way to open programs within Windows 7. Typically speaking, when utilizing Windows XP Mode and Windows Virtual PC, one does not want to depend on the use of such tools for graphic intense applications because they do exist within a virtualized environment.
The other possibility mentioned in the previous comment on this thread is to create a dual boot, or multiboot configuration between Microsoft Windows XP and Windows 7. The first step to note when prepping for a dual boot environment is to ensure you have a separate location for each operating system you intend to use. In this scenario you will want to have one partition for Windows 7 and a second, separate, partition for Microsoft Windows XP Professional. For a helpful video of how this process is performed, please click here. Another helpful resource is the multiboot step-by-step guide Install more than one operating system (multiboot.)