FriendlyKiwi already gave you great info, but I'll add my two cents. Although the frequency bands can vary by country, a U.S. FM receiver will work fine in Europe. I brought my 3 series from the U.S. two years ago, I have driven it in four countries here and the radio works fine not that I use it much.
So basically, all you need to do is buy the new NAV maps and you'll be fine.

As an aside, you'll often hear that the European Bimmers are different from the U.S. models. This is somewhat true. From a quality standpoint, there is no difference and in at least one way ours are much better... namely the fantastic U.S. BMW warranty. The warranty here is only two years compared to the five that my car had. This was an issue at the dealer when I had a problem because, unbeknown to me at the time, exporting your U.S. car negates the warranty. Thus your 2008 is already out of warranty locally and they won't honor it here. Also, U.S. models have governors in the electronic ignition so it will have a lower top speed than local models but really, even on the German autobahn, your opportunities to use that kind of speed are extremely limited and this is not an issue at all in my opinion. Finally, and this is important, when registering your car here it has to go through a rigorous inspection... you won't believe it until you see it... and the inspector will have all manner of issues with things like the location of the engine number being in a different place, the color of your turn signal lenses and so on. In the end, after a bunch of grief, I only had to have my headlights adjusted as our standard is different than the local one.