You've had to do this twice, so remember for next time if you get wonky behavior: =x11-base/x11-drm-20070314 works. x11-drm-20071019 and now x11-drm-20080710 do *not* work with the hardware on cabinet, and are masked in /etc/portage/package.mask. If a new version of x11-drm is released and causes an error message that drm is not supported, the solution is to downgrade x11-drm.
Alternatively, it appears those two versions are marked unstable, whereas 20070314 is marked stable. You may have had to switch to unstable to get a working version a year and a half ago (explaining why you have ~x86 in package.keywords), but the version you want is currently the latest stable version. Fix that.
In case anybody is randomly coming across this page, your graphics controller lists as "00:02.0 VGA compatible controller: Intel Corporation 82945G/GZ Integrated Graphics Controller (rev 02)"
[Hopefully this was the cause of my other trouble as well as causing a failure in graphics acceleration that I never observed as I don't rely on it often...we'll see.]