If you want to delete partitions on your hard drive that are not the system drive (C:) then you can use Windows Disk Management to do so. Just be sure that you have backed up any data that you want to keep since everything will be erased. You can also use Disk Management to create and format new partitions.
If you want to delete your system partition then you will have to boot with a bootable disk such as your Windows CD. Then you can begin the installation and when it gets to the part about where to install Windows you will be able to delete and create partitions there as well. Since you won’t be using your system partition this will allow you to delete it. If you don't want to make a new one after deleting it then you can simply quit the installation after that step.