Macworld's running a fantastic "Leopard Survival Guide" series, covering little-known Mac tips of all sorts, like how to customise the welcome text in a new Terminal window:
Open Terminal and enter
cd /etc, press return, and then type
sudo pico motd. That second command launches a text editor and loads a new file called motd (Message Of The Day). Type whatever you like for a message (for instance, "Welcome to the land where text is king"), press control-X (for Exit), press Y (for Yes, to save changes), and then press return (to accept the file name, which will be shown as
motd). From now on, new Terminal windows will display your new greeting, right below the date and time of the last login.