If the system is capable of booting of a cd, that is the best bet (you may need to adjust the boot order in your BIOS). This will load the install on the CD automatically and you can go from there. A few things to think about are: Windows XP needs to be "activated" which means giving micrsoft a load of info about the computer. I am not sure if the activation process checks to see if the serial number you are using has already been registared to another computer. Second if the Windows XP disc you have just lying around is from a major PC vender like Dell, Compaq, Gateway etc... it will check the system to make sure it is being installed on the proper machine (or at least thats the way it used to work) If none of these things bother you then good luck with the install. But if your having second thoughts you might want to go with a free OS such as Linux or FreeBSD.

Have Fun