Go into your BIOS settings (accessed by a one or some of several key combinations - try Goggling if you can;t find it easily) and change first boot device to CD. Restart and if necessary "Press any key to boot from CD..." Formatting (and partitioniing) is part of the installation process.
Sorry if this is obvious, but do remember that formatting your hard drive will destroy everything on it. That includes all your software and your data files. Be sure to back up data, and check that you've got all your software and driver CDs before you do it.