Some of you might have seen this on the dot, but there goes.
A flaw has been detected in the Athlon/Duron chips, which can cause instabiliy, it's supposed to get worse when combined with the use of an AGP videocard.
anyways the workaround is to append mem=nopentium to your lilo command line, or your lilo.conf.
This explained why I was unable to use AGPx4 on my mobo, after the fix - no problems. but beware, preformance might take a slight hit due to the nature of the fix/flaw, as it has to do with buffer size (I think).
www.gentoo.org has the juice, and if you are not man enough to fix it yourself, no worries, Alan Cox is making a dynamic workaround for the future versions of the Linux kernel, so the fix should be included in a kernel tree near you sometime in the near future.