Boot with your XP CD and refuse any recovery, repair or upgrade option. You can elect to format the drive.
If you only have a recovery disk from your manufacturer, that does a pretty effective job of re-creating your machine as new.
Before taking this step you may want to do a little research on the XP Files and Settings Transfer Wizard. See if there are any settings you would like to keep. It can be selective.
If you have downloaded driver or firmware updates in the past for your devices, make sure you make a copy of the original files you downloaded, (not the drivers themselves, the whole package) so as not to have to go through that process again. If you did not keep the files, you may want to look in Date Modified Sorted order:
c:\windows
c:\windows\system
c:\windows\system32
c:\windows\system32\drivers
See if there is anything there that rings a bell and write it down on a list so that you can go to the manufacturer's Web Sites and renew your driver and firmware files. It helps when doing this to turn "baloon tips" back on if you have it off.
I make a point to backup my hal.dll file. This is a hidden system file in c:\windows\system32 that among other things determines whether your system license has been activated. After XP is installed, from safe mode, rename the new hal.dll hal_old, and copy back your saved version.
Best of luck.