I guess I'm talking to myself heh.
I found a post which seems to indicate that things are not as simple as a bios update...
"Disclaimer: I am numbnut.
The 1.1 version of the Xbox is certainly designed to be Palladium Lite. The concept is that no code is executed unless it matches a one way hash signature. The only exception is the boot ROM (512 bytes) which lives in the nVidia-designed MCPX chip; this is used to validate the next code to execute, which validates the next code to execute and so on.
Unfortunately for MS (and perhaps nVidia), they chose a hashing algorithm which already had a known flaw. The hash, which works on QWORDS (64-bit quantities) is completely insensitive to b31 and b63 of a QWORD both being inverted.
Doubly unfortunately for MS, the VERY FIRST DWORD of the hashed region is the entry point, and contains a long relative jump. The effect of flipping b31 and b63 on this QWORD is to retarget the jump to RAM.
Triply unfortunately for MS, they have a small interpreter built into their ROM code, whose instruction set is capabel to to IO amd memory r/w before the bootrom is validated and executed. It was trivial to add some memory writes to the interpreted code stream to prep the memory targetted by the modified jump with a jump back into the flash.
The end result is perversion of the hashed region in a way invisible to the hashing algorithm, and execution flow jumping to arbitrary code in the flash.
I urge anyone interested in both the technical detail and the larger issues raised by this to read the threads on
http://www.xboxhacker.net as this is a much larger issue than simply another Xbox crack."
The initial hash "lives" in the MCPX as stated above.
Numbnut states that basically he flipped some bits to get the code to "jump into RAM" and "prepped" the table that would be jumped into via an interpreter.
The problem is that these "flipped bits" live in the MCPX, so something must be done to get the MCPX to go ahead and flip the bits.
E.G. some external wiring or hardware.