Thanks for the advice netllama and piotrq!
I actually found the problem was with the /etc/gdm/gdm.conf-custom file that was mentioned in that link. I had previously (when I first setup beryl) followed a tutorial that told me to enter an xgl server in that conf file. I commented out those lines, restarted and presto!
Thanks for the troubleshooting help! =D
ps- this command: "gnome-xgl-settings --disable-xgl" doesn't work in Ubuntu.