You can probably just pop the disc in and restart your comp, run the disk from CD and act like your installing a fresh OS but hit repair instead to just redo the OS and keep all your files. But if you want to completely wipe your drive, just do the same method and when it asks for the install location you can also tell it to delete the partition and format it. Make sure you have your CD drive above your hard drive in the boot order in the BIOS before this.