Go to
http://www.malwarebytes.org/ and download the free edition of Malwarebytes by clicking on the blue button on the left of the page, and save to desktop.
Install Malwarebytes, update it with the latest definitions and then set it to do a "full scan" and let it delete all and anything it finds.
Reboot, and Vista Guardian should be gone.....if it is still there, boot into safe mode and run another full scan, then reboot.