That makes sense. I guess then you are right Arty, it would probably would make most sense to get the relocation panel from BMW. I'm in South Africa, so I just hope the dealer doesn't rip me off - they tend to do that here :-)
burnhamd: Thanks for the link to the guide. I'll have a read through it. I want to properly understand the system before beginning the project. I also want to build the IBUS interface and be 100% sure about its use before I even buy any of the carputer's components. I'm just a bit worried about the double din bezel for the LCD - so far from the searches I've done the prices seem to be rip offs, considering it's just a piece of plastic.
One more question: Does anyone know if the e90 also uses the I-BUS i.e. if I design the system for my e46, and then decide I would prefer it in my e90, will it be easily done?