Reg00 should not be thirty two thousand mega bytes! It overlaps all the other mtrr regions and I can't add a write combining line.
Well .... some bios just suck (as an example I can see my notebook quick checking the ram up to 5GB, however I have only 4GB installed and it eventually decides that I really only have 4GB and settles with that) ... have you tried to update the bios to the latest version or maybe downgrade it to a previous version (if the bugs solved or features added don't affect you).
While you are at that maybe you can pass a parameter to the kernel and tell it to identify itself as windows vista or xp to the bios with the acpi_os_name="whatever" parameter (you will need to check how the different OSes identify themselves) and check if anything changes.
Dredging up this old thread to say that the cause of the problem was traced to a faulty nvidia GPU.
Windows 7 was installed on the same computer and experienced similar stability problems. The GPU was swapped for another and all stability issues have now disappeared.
Needless to say I'll be buying ATI from now on.