Reboot your computer. When GRUB pops up, it may say "Press ESC to enter menu", or alternatley you may be kicked to the menu if you have multiple OS's installed. Either way, when you get to the OS selection menu, select the menu option (kernel choice) that has the word "Recovery" in it.
Once that's loaded, choose the "drop to root terminal" option (to that effect, the exact wording may be different) from the imtimidating blue menu that pops up.
From there, type the following command.
sudo apt-get purge compiz compiz-core
Hope that works...