I'm pretty sure the answer is this:
Other than the installer, XAMPP is kinda Windows agnostic. It doesn't really 'install' in the traditional Windows OS sense.
An easy thing would be to simply copy The Start menu Section for XAMPP from the Administrators Start Menu Programs to 'All Users' >Start Menu > Programs in Explorer. (you may want delete the Administrator's entries after you ensure it works right, as you prolly will wind up with two sets of entries in the and the Desktop)
All Users is where XP puts programs that allow you to select what users to install for during setup.
The folder is: C:\Documents and Settings\All Users\Start Menu, ditto the desktop icon that starts the XAMPP control Panel if you want, copy form one to the other. (its actually in the XAMPP section anyway)
The parts of XAMPP all run as exectables and their configuration files are normally all in the c:\xampp folder, so you should be OK.