you should have a red recovery floppy,if not get one from the download link for your computer click here
xp will be pre installed.there is a hidden sector on your hard drive containing the operating system and drivers/programs etc.
click start/all programs/pc tool kit & services,here you should see "smart restore" use this to install or remove any pre installed software.
you should also be able to create your own master discs from the hidden partition using "my cd writer" or similar in all programs menu.
if you do make your own,check them for errors afterwards as when you create the master cds you no longer will have the hidden partition.