After you get your machine ready, boot with the Windows XP disk and start a new install. The installer will start to run, and it will find your previous version of Windows already installed and ask you if you want to do a new installation, or repair your current installation. Here is where you choose to do a repair install. The installer will run, and it will appear to be doing a complete new installation, but after it is done, all your programs and data will still there, but the install will now work with your new hardware.
Is this as good as a complete fresh install, sometimes yes, and sometimes no, but it is worth trying to see if it works well in your case, will save a lot of time and reinstalling if it works out good for you. Most of the time it will. Do not forget to reinstall all your new motherboard drivers, GPU drivers, etc after your repair install.
As an alternative you can save the data that you really need and just do a fresh install of Windows XP , that way you get rid of all the drivers and files from the old hardware. A fresh install is always better for the OS anyway because you get rid of the old baggage and you start out new and it makes it like the hdd is new again.