Congratulations! That's a beauty!
The supplemental ///M manual can be found here. No differences for 07/08 (as far as I know the car did not change, and the 07 supplement looks exactly the same as the 06). The M supplement covers the ///M features and differences; the rest of the car is the same as the Z4.
If you're looking for the "regular" manual, that's the just the Z4 download from the BMW site
or from this link. The Z4M has some extra features, but it's basically a Z4. Unfortunately the regular manual doesn't cover navigation, and it references a separate Nav/Computer manual which the BMW site doesn't have available for download!
Here is the list of all the manuals you should have. The only thing I can find for the
computer/nav/sound system is this. This is
not the Z4 computer/nav manual, but the computer functions appear for the most part to be very similar (some exactly the same) to those in the Z4. I think it should help a bit to point you in the right direction at least to get started.
The best bet probably would be to find someone near you with a full Z4 manual set and take it to a copy center....in the meantime, see if this helps.