It is doubtful that Windows XP will work on a PI.
Unless you have a retail version of XP and you removed it from the computer on which it was first activated and could prove that to Microsoft you couldn't use it even if the old computer could run it - which it cannot. It wouldn't authenticate.
You can't just move a hard drive with Windows installed on it from one computer to another because the registry would be completely wrong - set up for the computer it was in - so that wouldn't work even on a computer that was capable of running XP.
Minimum Requirements for XP
Here's What You Need to Use Windows XP Home Edition
PC with 300 megahertz (MHz) or higher processor clock speed recommended; 233-MHz minimum required;* Intel Pentium/Celeron family, AMD K6/Athlon/Duron family, or compatible processor recommended
128 megabytes (MB) of RAM or higher recommended (64 MB minimum supported; may limit performance and some features) (you really need 512 MB for it to function above a crawl)
1.5 gigabyte (GB) of available hard disk space.*
Super VGA (800 × 600) or higher resolution video adapter and monitor
CD-ROM or DVD drive
Keyboard and Microsoft Mouse or compatible pointing devicehttp://www.microsoft.com/windowsxp/home/up...ng/sysreqs.mspx