This site should help, once you find the disk:
http://www.windowsreinstall.com/Left column has the different versions of Windoz. Click on your version and it will take you to a page which details the various installs.
Basically, if you want to wipe everything and start over, backup all data that you want to keep, shut the machine down and disconnect all peripherials, such as printers, scanners, cameras, etc..., then boot from the Windows CD and follow the instructions for a new install. Format the drive, set the partitions (if needed), and let the program finish the install. Then download or install all the latest drivers, and then all the stupid windows updates. Install peripherials, anti-virus, and applications software.
If you're good or really lucky, it will take less than a day
Another option, is to buy another hard drive (pretty cheap these days) Do your fresh install. Re-install the old drive, transfer data, then wipe that drive (format/partition). Then you can use the second drive for backups and additional storage.