If its a fresh install, just start over, erase the drive and install again. If not and there are things on the drive I can describe a way to use single user or terminal from recovery to extract all information first then wipe and reinstall.
How were you managing to install Windows 7 before anything else? If the drive is truly wiped clean and properly partitioned and formatted, I would imagine the installer is the problem. Where did you get the installer or did you make it yourself?