Ok, I have not tested this yet, as soon as I did I will update this posts, so please if you try it and have good results (or bad) post it on comments.

First get the ATI drivers from its page, here:

http://ati.amd.com/support/driver-sp.html

follow the instructions given there for CentOS

Then you will need the Fedora Extras repository enabled in your yum configuration.

So create this file:

/etc/yum.repos.d/fedora.repo

with this content.

[extras] name=Fedora Core 6 Extras mirrorlist=http://mirrors.fedoraproject.org/mirrorlist?repo=extras-6&arch=$basearch enabled=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-fedora-extras gpgcheck=1

Remember to turn this repo off once Beryl is installed, I think is better that way, so you do not mix packages when updating your CentOS

Then save it and run.

yum install beryl-gnome

That should be all, please remember to comment here if you get any good or bad results.