Use either SystemRescueCD or boot to any Linux LiveCD and open a terminal. To do this, either type startx and Enter or click on a terminal icon, respectively. At the terminal, type
dd if=/dev/zero of=/dev/sda bs=4096 conv=notrunc,sync
and wait until a response is received that ends "xxxMB/sec"
Then, one can partition using gparted, fdisk, Parted Magic, cfdisk or whatever.
This writes zeros to the drive for a clean istall. Best wishes and welcome to linux!