I can recommend getting an external USB hard drive and a copy of Acronis, make a backup of C drive on your external drive before doing anything else then you will be safer. Acronis helps you to make a bootable CD that allows you to restore from the USB drive if all else fails. I also recommend EA8 to back up all your emails and OE account settings on the usb drive
Often the restoration info is stored on a hidden partition on the HDD. You are normally provided with a program to create your own CD's. If you don't create your own CD's and try to install Windows from another disc or format the HDD, you'll need to purchase Windows again. If you have an OEM and you need to reinstall specific files to fix windows, good luck, I usually have to reinstall Windows entirely.