Can't compile for KDE

Hi, I'm trying to compile Gwenview (but this also happened while trying to compile other programs) and when launching ./configure I get this error: checking for KDE... configure: error: in the prefix, you've chosen, are no KDE headers installed. This will fail. So, check this please and use another prefix! The command "kde-config --prefix" outputs "/opt/kde3", so I've also tried with: ./configure --prefix=/opt/kde3 but the error came out the same. I've installed: kdelibs4-kde3-dev kdebase-kde3-dev and other dev packages but still I get the error. Any suggestions? Thanks Luca