Re: 2.6.26+ w/AMD K6-III/450 issues
Tried Option NoMTRR? I didn't think they were used so much anymore, but Xorg.conf's manpage makes it sound useful still.. Certain compiler optimizations (like SSE) on components related to X could be causing problems on an older processor like that. Could you revert to an older kernel and/or X? CentOS 5.x has been running 2.6.18 for ages. If you used their sources to build your own kernel, it should be safe to use (so long as you keep up with it).