I heard rumors WMDs where used. However, why would Sadam give WMDs to the Serbs who where fighting muslims. Sure, Saddam wasn't above killing muslims but he tended to have some kind of reason.
Now, giving them to the muslims (extremists) would be *interesting* (while I see no good reason for that either, maybe sneaky guy manage to steal it?).
I used to subscribe to a magazine called Air Forces Monthly, mostly because it had a shitload of pictures from aircraft from the collective armpits of nowhere.
When NATO finally when into Bosnia and Kosovo, some photos started leaking out that the Yugoslav's had been doing some work for the Iraqis repairing their MiG-23 Floggers. This was all based on some pictures someone had taken of a tarmac that was supposedly in some northern Serbian airfield of some Floggers with the roundels scraped off.
Supposedly, some NATO intelligence service thought they were Iraqi Floggers due to the radars or something. Myself, I think it was a load of crap, and just some people jumping at shadows.
I personally think that the Serbians probably could've gotten chemical weapons from some dump somewhere else at the end of the Cold War, and then used them. That's all I can think of.