1) Are you certain your hardware suppors XP?
2) If so, you need to install all of the appropriate drivers for XP (chipset, sound, display, etc)
Just a step further on Allan (no thunder stealing intended), in case you do not know how to locate and install them, you need to locate either the;
Make and Model of your computer if it is a big name brand i.e HP, Dell. e.g Dell Dimension 2400
or
The Make and Model of your motherboard if it is a custom PC e.g Asus P8Z77
And then go to the manufacturer site and locate your product using their search functions to get your drivers. At this stage you will be able to tell if your computer is Windows XP compatible if it is listed as a Operating System in the list when it asks which OS you have installed for the drivers.
