The basic concept is that frames can only be forwarded out a port according to the Hardware address table. The exception is that a frame is forwarded out of every port excepting the one it received the frame on when the destination hardware address is not in the table. This makes monitoring network traffic difficult. In order to monitor with a switch, you'll need to create a SPAN session that tells the switch to forward a copy to your computer.
The following will setup port 1 on a Cisco Switch to monitor Fa0/4:
port monitor Fa0/4
You can also setup a port (Fa0/1 in this case) to forward data destined to a particular VLAN (VLAN2 here):