Now that you mention it, I had that problem with my old motherboard (VIA KT133A). I had to use the nopentium trick, but I lost some performance.
Now I use a KT266A motherboard and guess what... I forgot to add the nopentium line at GRUB!! I hadn't noticed before precisely because my system is running rock solid. I switched to RH 7.3 from RH 7.2, as well. Perhaps that had something to do with it. But I've had no problems with the three kernels I've tried (2.4.18-3, 2.4.18-5 and 2.4.18-10).
I remember from a while back that nVidia and AMD blamed each other for this bug. It seems both pieces of hardware tend to fight overa certain part of the AGP texture memory, hence the hard-lockups.
No official fix has been released, AFAIK.
Use the source, Tux.