You will have the same Multiplayer modes as on the PC.
I'm glad to hear that Napoleon TW for Mac will have multi-player. I was disappointed with the lack of multi-player on Empire Total War.
I love military history (an amateur hobbyist, not as professional) but I greatly prefer the military-political wars of the 17th-18th centuries. The great wars of Maria Theresia, Frederick the Great, and of course Mad King George (whose ineptitude and tyranny resulted in the formation of the United States). Plus I love the fact that you could play as the (non-European) Maratha Confederacy in Empire!
Napoleonic Wars is also an interesting period... but there is only so much you can accomplish in empire-building and "world conquest" strategy when your historical time frame is about 15 years. What made the Nap era exciting and unique was that the borders of Europe changed drastically in a matter of months (or a few years) due to Napoleon being able to wage lightning-fast conquests/invasions of his neighbors (sorta like a blitzkrieg-style warfare of his time).