alx - Thanky.
re: difficulty - The difficulty for each porting task varied from project to project. The source code to some emu's is very clean/understandable/portable and doesn't take long to make the necessary changes. e.g. When the source code to NeoPop was released, I released my port of it in about 2 hours. Other emulator source-bases are very messy/tough to understand/ or present unique porting challenges in the way they handle their audio and video buffers.
re: source - read thread
re: plex86 - Bochs is much more compatible. Plex86 was not at a point where it would run anything useful. Even now, if I had to choose between the two, I'd go with Bochs. It doesn't matter how fast something runs if all you can do is play Infocom text adventures on it.
re: tutorials - I'm sure there's plenty of existing, useful information in the forums of places like this, xboxhacker and various other places on the web. If someone has specific questions for me wrt programming for the XBox, I'll try and answer them.