The libpng should be no problem. What was the exact error you got? remember you should also install the "devel" packages of libpng for aMule to compile fine using it. The problem with aMuleweb crashing was on old versions, it would crash if some image did not exist, I think that is corrected in recent CVS versions. Get the latest CVS from amule.hirnriss.net, compile it and report back.
Regards.