OK, this is a real pita. I found the repository containing tcpdump, but get errors when trying to install it using the Application Manager. When I use xterm and do "apt-get install tcpdump" I see the errors are related to libpcap and ncurses-bin.

After more research I see that ncurses-bin is already listed as an installed application in the Application Manager, but the size is shown as 0 kB. It won't let me uninstall that, and I can't install it properly.

Grrrrr......