This thread may be a bit old, but I have just spent a few weeks batling different Linux distros after buying an X1650 Pro AGP card. Before removing the old Radeon 7200 AGP card, sabayon booted off the live DVD (Linux User magazine distro). The new X1650 card would fail to boot about half way through. Lock up with a repeat beat from the sound card.
I tried every Linux I could find. Only Debian, openSUSE 10.3 and Ubuntu 7.10 would boot with the X1650. (BTW: the computer also runs Win 2K and Win XP, which have no problems with the card.) However, no amount of hair pulling would get the ATI drivers to support 3D acceleration. The Mesa drivers would not release for the fglrx drivers to load. Diagnostic with 'demsg | grep agp' indicated that the AGP aperture was not being assigned (that was on openSUSE and Ubuntu). The Gigabyte BIOS did not list any AGP options... that was until I found off their web site, that the AGP configuration is "Advanced" and needed a <Ctrl> <F1> at the main BIOS page to reveal it. Initial AGP Aperture was 32MB. BIOS allowed 512MB (the X1650 on board memory). Setting the aperture in BIOS suddenly enabled full 3D acceleration in Ubuntu. And then in openSUSE).
The finale is that with the aperture set, sabayon now boots fully off the live DVD... an installation is now underway.
SO: note to sabayon developers: the bootup will lock up if an AGP aperture cannot be set. This hang occurs with sabayon and Mandriva. openSUSE, Ubuntu and Debian do not hang. "Bug" is in hardware detection and recovery.
Note to ATI AGP card users: set the aperture in BIOS before trying sabayon. If you can't find AGP settings in the BIOS, check the manufacturers web site... maybe try <Ctrl> <F1>.