Windows XP Dual boot Windows Vista

If you would like to try out Windows Vista on a Windows XP, you may want to use dual boot to avoid any complication arises and revert back to previous platform. This can be done, guided, through Microsoft MSDN site:

Creating a multi-boot configuration that includes Windows Vista
To create a working multi-boot configuration, install the oldest version of the Windows operating system first. Then, install each newer version in order. Every new Windows version preserves backward compatibility for starting earlier Windows versions.

To create a multi-boot configuration that includes Windows Vista, you must have at least one partition for each earlier Windows version that you install. Follow these general guidelines: • Create at least two partitions. Use one partition for the Windows Vista installation.

Note If the partition for Windows Vista is already formatted, make sure that it is formatted by using the NTFS file system. However, we recommend that you use one of the following methods: • Create the second unformatted partition.
• Do not create the second partition and leave the space as free space. Instead, create the second partition during the Windows Vista installation.

• If the computer does not have an operating system installed, install the oldest Windows version first.

Note Install Windows XP before you install Windows Server 2003.
• Run the Windows Vista Setup program. Install Windows Vista in the free space or in the existing partition. You can run this Setup program in the earlier Windows version, or you can start the computer when the Windows Vista disc is in the CD or DVD drive.
After Windows Vista Setup finishes, you will have a correctly-configured, multi-boot environment that includes Windows Vista and the earlier versions of Windows. The Bootmgr boot menu that appears resembles the following menu:
Microsoft Windows Earlier Windows Operating System

Via Windows Vista no longer starts after you install an earlier version of Windows