I understand how you are worried about getting into Macedonia via a car. But don't worry, Macedonia in 2007 isn't like Iraq in 2007. And Macedonia's neighbors are tame too.
I think they got tired of fighting in the 1990s. It wore them out. So it's not dangerous.
I would take a path down the Croatian coast, thru Montenegro, and then into Macedonia via either Albania or Serbia.
Albanians are more pro-American than Serbians. Last week the Albanians received George Bush with open arms. Few countries do that today.
On the other hand, Albania is more poor than Serbia. Poor people might be more desperate and more likely to steal from you. However, I wouldn't want this. Many Albanians drive Mercedes and so if you come in with a nice car, it's no big deal. Same goes for Serbia.
I'd probably take the Serbian route since I did the Albanian route in 2004.
Tell me how it goes!