Monitoring port vlan1 just gives you the management traffic for the switch, because interface vlan1 is the management interface which also holds the ip address of the switch.
There is no easy way (that I know of ;-)) to monitor a whole vlan. But you can configure multiple [tt]port monitor fa0/x[/tt] statements, so that you can monitor all ports in vlan 1. A simple 8tt9no port monitor[/tt] will remove them all.
Cheers *Rob