Problem with GTK using the display

[<naderz attbi com>]

I have just downloaded and successfully installed the necessary packages to
run "ethereal" on an iMac (Mac OS 10.2).

However, when I run ethereal I get the following message:

Gtk-WARNING **: cannot open display:

I have tried setenv DISPLAY :0.0 to no avail.

I am fairly new to this so any help is appreciated.