Just remember that "VLAN separation" is a misnomer. The VLAN tag is inserted in the Ethernet Frame, http://upload.wikimedia.org/wikipedia/commons/2/23/TCPIP_802.1Q.jpg There isn't anything magical about an 802.1q tag.
It is possible to overload a switches CAM table which effectively turns them into hubs. Most modern day switches have enough memory allocated to the CAM table, search for "cam table overflow" for more info. diana
