|That can mean the XP cd is scratched or in some way damaged or it can mean the cdrom is starting to fail or its lens is dirty. It might be both. That is, a good cdrom may be able to read a slightly damaged cd.|
It's also possible you have bad ram or a problem with the hard drive. But I suspect it's the XP cd. Clean it with some alcohol or windex and a soft towel. You may want to get a lens cleaner cd for the drive too.
And if you mean it's rebooting and starting the installation process each time--that's because it's booting from the cd. Normally with the cdrom set as the first boot device, a bootable cd will give an option to boot from the cd or boot from the hard drive. When you start up the PC the first time to do the installation you want to boot from the cd. After that you want to boot from the hard drive.