1. Manufacturer's System Restore CDs
Many machines, particularly laptops, are now supplied with one or more System Restore CDs. These are different from Microsoft Windows Installation CDs and are designed to restore your system to exactly how it was when it left the factory. Use of System Restore CDs will completely destroy any other software and documents you have installed or created on the machine since it was new. A separate document contains information on how to make a back up of your own data files. To reinstall applications such as Microsoft Office, you will need to have your own copy of the original installation media for each program.
Instructions for use of the CDs should be in your machine's documentation. This normally involves booting the machine from a System Restore CD and following the onscreen instructions. This should be done with the machine disconnected from the network.
After using Sytem Restore CDs, you should install any Windows XP service packs later than the ones included on the CDs. If you are installing Windows XP Service Pack 2, you should do this from a CD rather than by online download (your local IT staff should have a CD for this). Connecting to the network (even for a few seconds) without having reinstalled Windows service packs will immediately expose you to external attack. You should also install up-to-date antivirus software before connecting to the network.