I have recently shifted to OSX environment, so don't know much about MacPorts.
Is there a way to tell MacPorts to pick already installed packages. For instance to install
sudo port install meld
its requiring hell lot of packages, including python2.6. But I already have python2.6 installed.
No there isnt. If you want to link against system installations then use Homebrew or compile manually yourself. Personally i prefer Macports because its completely isolated. Ive got plenty of disk so having duplicates doesnt bother me.