Hi all,
As soon as I posted this question, I found the answer. I'm not sure if this is the most efficient way, but it works.
After the query has returned the selected features set the first one to
var selectedExtent:Extent;
var newGraphic:Graphic=featureSet.features[0];
selectedExtent=Polygon(newGraphic.geometry).extent;
then loop thru the results combining the extents of each polygon as you loop
for each (var myGraphic:Graphic in featureSet.features )
selectedExtent=selectedExtent.union(Polygon(myGraphic.geometry).extent);
then zoom to the new extent, or a zoom factor, or whatever you choose.
Thanx forum,
Eddie