> could we not attempt to match the signature on the firmware so the Zune would accept it?
Easy to attempt, but hard to find (ie. many years of calculations) unless you are very lucky. Check other threads, this has been discussed before.
BTW: The core firmware uses the "SHA-1" hash. I suspect they are using the same for the XNA game library DLLs.
http://en.wikipedia.org/wiki/Sha-1#SHA-1_algorithm