Arduino Serial Communication Problem

My arduino board is not being recognized by the arduino environment. I can't select it in the serial port because it does not show up. Is there any way that I can find out whether or not the board is fried? I'm still getting power and the last sketch that I uploaded to it (yes it was working at one point) is still on it. I need to figure out whether I need a new one or if I can somehow use this one still. I'm new to all of this so if this doesn't make sense I apologize.

What kind of Arduino board?

What operating system?

Arduino Diecimila

Mac OS X Intel (leopard)

Try doing:

ls /dev/tty.*

from the Terminal when the board is connected and when it's not. Does anything extra show up when the board is connected?