Its odd, the PS1 was relatively easy to emulate as its CPU code was relatively strait forward to interpret in to X86 code, also the GPU was reactively basic and easy to get a PC GPU chip to do the same work and even if it could not do it all some was just passed on to the CPU, even the sound not that hard, also people just ripped the BIOS to make life easy. So all in all the PSX is easy
Unlike the N64 that is a relatively odd system and to run any of the games that were coded to utilize the full 64bit power of the system you have to have a CPU with SSE to map the R4300 register to the SSE stack and many other odd tricks like that. Even the GPU is relatively odd and in many situation companies like Rare were coding the system at very low levels. There is still no fully working N64 emulator out even now.
So if we go by this the Xbox should be relatively easy to emulate as the CPU is just a Celeron and the GPU is a old GF chip. I think it was something close to GF3 but missing the odd bit like the GF2 but also with more pipelines like the GF4. I would like to know the actual problems they are encountering.
What is the best Xbox emulators out? I think ill have to email them and offer a hand, My English may be terrible but perhaps I will finally get to utilize something I learnt at when I was at university.