dia+osx? help!

["botkiller promo" <botkillerpromo gmail com>]

I'm confused ... I've installed dia via darwinports on OS X 10.4.9 - but how do I run it?  I am new to this, I apologize - but I can't find anything on how I run dia after all this.  In terminal, if I type dia I get (dia:16671) gtk-warning **: cannot open display: , and I'm kicked back.  What am I doing wrong?  Do I need to run dia in X11?  Did my install not complete or something?  I know that dia is installed, but this is quite annoying... thanks. 

-brian