"Serbs are Muslims, are they not?"
Excuse me? What planet have you been living on? Majority Serbs are Orthodox Christian. There is a Muslim minority in Serbs (for example the majority Albanians in the Serbian province Kosovo). The war in Bosnia during the 90's was also between Serbs (Orthodox as I said above), Croatians (Catholics) and "Bosniaks" (Muslims). Maybe you should read up on the Balkans before you comment.
"There is a Muslim minority in Serbs"
Sorry, typo..should be "There is a Muslim minority in Serbia".
Note, that the issues there are highly contested, lots of blood spilled, and I can't vouch for any info being 100% true.
Anyway, for what it worth...
From another source: http://home.zonnet.nl/gerardvonhebel/yugoethno.htm
Ethnography of Yugoslavia as it was in 1991
http://home.zonnet.nl/gerardvonhebel/yugogrowthanddecline.htm
The Yugoslavian growth and decline
1813 1815 1878
1908 1913 1923
19431955 1999