You may not have Compiz set to load from Emerald, try right clicking on the blue Compiz icon and go down to "Select Window Decorator" and click on Emerald.
Then click reload and try and select a theme.
If that doesn't work try right clicking on the blue Compiz icon again and go to "Select Window Manager" and select Compiz.
Then click reload again.
Now, if that doesn't work you probably skipped to the graphical installation like I did.
Restart your computer, before you log in to your desktop go down to the very bottom left hand corner and click on the Icon of the box (Hard-Drive? I don't remember off hand.) Scroll around to "Acceleration Manager" and then click on it, log in like normal.
It should then ask you for your root password, go ahead and type it in.
Soon a window should pop up with something like "No Acceleration, AIGLX and XGL", try AIGLX acceleration, click next, or ok. Whatever it says.
You should after that be prompted to press CTRL+ALT+Backspace, go ahead and click ok and do so.
It should work after that.. If not I have no idea.