Got some tips, articles that could point me in the right direction?
One example is XQuartz the X11 port for OS X http://xquartz.macosforge.org/trac/wiki/Releases
If you know what are you doing probably this is a good point to start, and if you need other libraries then you should look there too.
Otherwise, learn Objective-C and Cocoa, and rewrite the user interface. Works better when the application is well modularised to begin with.