re : using libs installed with macports to build a tarball

Hi there I noticed an odd thing. I've built and installed liblrdf (ardour dependency) in /usr/local and when I run scons in ardour's directory (equivalent to './configure && make') it says it can't find liblrdf. I've reinstalled liblrdf with "--prefix=/opt/local" and now it works ?!? I don't really understand the priority between one Include directory and another so do I have something particular to know when I want to mix a macports installed soft or lib and a "hand-made" build ? Rémi Leopard, Macbook 2GHz Intel Core 2 Duo