As other posters have stated, yes, you can run Microsoft Windows XP and Microsoft Windows 7 in a dual boot configuration so long as each operating system is installed in a separate partition. To learn more about how to configure this environment, please navigate to the following link: http://technet.microsoft.com/en-us/edge/Video/ff710733.
You should be able to share the essential document files between both systems. Some system files, for security purposes, will not be accessible for Windows XP and vice versa for Windows 7.
One could also choose to utilize Windows XP Mode and Windows Virtual PC should he or she desire. Windows XP Mode was designed to simplify the transition process from Microsoft Windows XP to Microsoft Windows 7 by offering a virtualized environment for applications that will only work within a legacy operating system. To learn more about Windows XP Mode and Windows Virtual PC, you may want to go here: http://www.microsoft.com/windows/virtual-pc/get-started.aspx.
Windows Outreach Team – IT Pro