You can limit the broadcast either based on the bandwidth or on the number of packets per second.
In the broadcast based method, you can configure the percentage of total available bandwidth that can be used by broadcast/multicast traffic.
Packet-based broadcast/multicast suppression measures broadcast/multicast activity relative to the total number of packets received on the port.
I am sure the following configuration guide will clear all your questions about broadsact/multicast suppression on a Catalyst port.
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/rel_6_3/config/bcastsup.htm