technical multicasting question

Hope someone can help on this. with IP multicast do you need to go through a router running IGMP and CGMP to populate the switch running CGMP to keep the switch from treating the multicast as a broadcast or is there a way I can have server and hosts on the same switch and the switch recognize the IGMP request? secondly if you are running application layer multicast wouldnt that just be like a multi-unicast session where the host will send the same packet to each joined client over its link (basicly it would be talking to each client individualy apposed to only sending the data out once).