How do I erase my Hard Drive
Boot your system from the Mac OS X installer disk and run Disk Utility from the Utilities menu.
partition it into 4 partitions
Disk Utility can partition the drive.
install OS 10.6 onto 2 of these
Either run in the installation process twice, selecting each partition in turn, or install on one and use a cloning utility such as Carbon Copy Cloner to clone the installation from one partition to the other.
and update one OS to 10.6.6???
Run Software Update (which will now get you 10.6.7) or download the 10.6.6 Combo Updater from Apple's web site.
Regards.