|Before installing XP on this laptop which I assume came with Windows 7, are you sure you can get all the necessary drivers for Windows XP. Drivers may not exist for newer hardware.|
When installing multiple versions of Windows on the same system, it is normal to install the older system first. There is a good reason for that as the older version knows nothing of the new version and will over write the system files used by the newer version preventing it from working. These system files have nothing to do with which partition you use, they are in the root folder of the primary hard disk and there is only one set of files regardless of how many different version of Windows you install..
The only way to get XP onto a system that already has Windows 7 without disturbing Windows 7 on it is to install it onto a separate physical hard disk and temporally disable the Windows 7 hard disk. You will then need to manually configure a dual boot system.
A much easier solution if the version of XP is Professional is to install it in a Virtual Machine. That takes care of the the driver problems you may have with installing an older version of Windows on a newer computer.