Just a note that today, 23 June 2009,
lxnay changed the contents of the ati-drivers-8.593-r10 ebuild in the SL overlay repository. To reiterate, the file name of the ebuild is the same but the contents have changed. The package ati-drivers-8.593-r10#2.6.29-sabayon in the main Entropy repository is presumably built from the new version of ati-drivers-8.593-r10.ebuild. You can read the details in my post:
Re: AMD Unsupported hardware watermark.