To proceed ahead, please check with HP if they have necessary drivers for your computer compatible with Windows XP. Once they confirm that they have drivers. Get a Windows XP CD and follow manual to install Windows XP.
Note: Kindly ensure that you backup all required data before you proceed with installation.
I am not the right person to help you with SAP.
Also, if you are keen on installing Windows XP to use SAP or something.
Then you can try using Microsoft Virtual PC on your laptop.