> Go and check what instruction has the Hex: f00fc7c8 it might be halt
 instruction
> or any wait. Try to run it on the NT system.

The 0xF0 is a "lock" prefix.  This instructs the CPU that the next instruction
should be executed atomically; the prefix is only supposed to be used with
certain instructions.  I don't know what the 0FC7C8 instruction is (the 0F is
a 386-specific prefix byte and I don't have the table handy) but it's probably
an instruction which is not allowed to be "LOCK"'ed.

I think the problem is probably that the "lock" prefix is causing one of
the CPU's execution units to lock the bus and never release it.  On a 486
this situation would simply result in an invalid-instruction trap, but on
the Pentium it apparently does not (or it might be that the instruction DOES
cause an invalid-instruction trap, but with the bus locked; the interrupt
logic might then be stuck forever waiting to stack the program state.

Still, it is disturbing that no Pentium OS can be written to be immune to
denial-of-service attacks.