Douglas
You have to configure your switch so that the port that your monitorising box is connected to receives all the packets that interest you. In the Alcatel switch we have this is called mirroring. You probably will need to do this before you can start sniffing as otherwise you will only see packets directed towards your NIC. I believe it is no longer necessary to put your NIC in promiscous mode as Ethereal (or others..) will do this when you set it up.
