Hey A.K.:
yeah, on my v1.2.1 double-clicking on the WireShark icon launches an instance of X11 then launches Wireshark inside that, similar to your experience of launching from Terminal command line.
If you update to 1.2.1, I don't know how 0.99.6 behaves, but starting with about v1.0.6, there was some "manual" modifications that you have to make with some path declarations so the program works right. And they have to be set up for each user of the application. I found out about it reading someone else's post about problems with Wireshark and some other smart guy on these forums had gotten the O.P. straightened out. That's as good as I can do for giving credit where credit is due.
You have to:
Go into Wireshark - Edit - Preferences
Select Name Resolution
Click 'Edit' 'SMI (MIB and PIB) paths'
Add new path: /usr/share/snmp/mibs
Find line in /Library/StartupItems/ChmodBPF/ChmodBPF that reads 'chgrp admin /dev/bpf*' is changed to 'chgrp staff /dev/bpf*'
This last item is if you do what the readme says when installing it, and put ChmodBPF in the startup items folder and you want regular non-privileged user accounts to be able to run it.
Now, to try to get back on track with the original post, I would just have to say that I would check whether the version the O.P. has, is in fact the v0.1 that is purportedly Tiger capable. If the O.P.'s version is a download from wireshark.org, it appears to me that the versions currently posted there only support Leopard.
