Windows Vista Help. Wipe Hard Drive, without Windows.old?

I tried again and again, but I just can not do it right. I would clean my hard drive and start all over again. I am running Windows Vista Home Premium on a Dell XPS M1720 (notebook). I insert the installation CD for Vista OS (came with the computer). So I restart the system. No start-up, I hit F12 (or ESC, I forgot), and have given the boot-menu. I say the system "BOOT FROM CD". I follow the instructions on the screen and re-install Windows. Whenever that happens, it keeps the Windows.old. I wish the process to erase everything on my disk, instead of keeping folder. This is a feature of Vista that I can disable? Or is making a Windows.old everytime?

Well, you deleted the previous installation or just installed it directly to the hard disk without deleting the current partition. Choose advanced mode> select your current C: drive and delete it. To continue with a new installation on the selected partition using NTFS format

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