Select the components, open Windows>Ruby Console, paste this one-liner and press enter.
Sketchup.active_model.selection.grep(Sketchup;;ComponentInstance).each{|ci| ci.transform! Geom;;Transformation.translation([0,0,-ci.transformation.origin.z]) }This will put all selected components on the XY plane.[/quote]
sdmitch, thank you. Just what I needed. Just have to be careful to copy and paste the whole thing, even the last } which is on the bottom line.