Hi Steve, welcome to the forum,
I understand your confussion mate.
Some of the problems come from BMW themselves, they say that the widescreen and 4:3 monitor system are "Professional", so it’s a reasonable assumption that you need the PRO disc, however, in this case the "Professional" means 16:9 or 4:3 colour monitor with dual tuner, as apposed to the 2" orange display (bussines).
What Nav Map disc you need depends on your car, your cars age and your Nav computer type.
So, if you have a e46, e39 or an early x5 then you have an I-BUS system and need the HIGH map disc, most of the newer cars use the MOST bus system for the Navigation system and for this you need the Professional Map disc.
This link give a better explanation about the I-BUS Navigation systems
http://www.xoutpost.com/articles/all-...ystem-faq.html
HTH