How can I format my computer using a regular CD-R/CD-RW?

That's easy... However you can not do it with any random cd/dvd. Do this, insert your Xp or Vista Os cd/dvd and you follow prompts to install a new installation. After that it would ask you iif you want a fresh installation or repair. Choosing a fresh installation Enables you to Format your Harddisk. After that you may not continue with the installation. Alternatiively you can download softwares from the internet to format it.... Use this option with caution though. Also make sure you have a backup of your important files. However formating it means u can not do stuff on ur pc unless you reinstall a Os.