Some people can't install Interarchy because their network admin won't give them the admin password for their machine. Interarchy needs the root access to install so it can bless the Ping, Traceroute and WatchTraffic commands (although WatchTraffic will ask for the root password every time for security reasons anyway and this hint won't help that).
Download and launch Interarchy 6, cancel the second dialog (the authorization dialog) when asked for the admin password and Interarchy will quit (after setting up most of the files). Reboot into single user mode (hold Command and S keys during boot), and then remount the root volume with write permissions by typing:
% /sbin/mount -wu /Note: If you have more than one volume, you might have to find the right one. Now type:
% cd '/Library/Application Support/Interarchy/'(The 'cd' command is shown as two separate commands to narrow the display width; it can obviously be entered as one long command). Type control-D to logout and continue booting in to multiuser mode, and Interarchy should work as expected.
% cd 'Interarchy Support.bundle/Contents/Resources/'
% chmod a+x Bless
% ./Bless Ping Traceroute WatchTraffic
Mac OS X Hints
http://hints.macworld.com/article.php?story=20021107054159625