Forti, 90C (not F) is the "maximum die temperature" for Athlon XP's 2100+ and below will operate at without thermal failure (it's 85C for the 2200+ and above (smaller die process)). Theses are AMD specifications. If your Mobo has thermal shutdown protection, it will shut down at these numbers by default.
Is it possible that he was running at 96C? Yes, but not without EXTREEME risk (ie, damage) to the Athlon XP die. His constant BSOD's were a symptom of a thermal breakdown and failure of his processor. Running at this temp. for any period of time will destroy it. As I understand it, this portion of the processor actually starts to break down on the microscopic level leading to permanent damage.
But just because it can run up to 90C, does not mean that's a good temp to run at. The higher your temp, the more performance hit you are going to take. That is why 65C is a good number, as it's roughly 2/3 of the max die temp. Keeping your temps at lower that that number, will help your overall stability and performance.
