Occasionally, the Finder will remember a shared server in the left hand Finder pane. This sort of persistent Shared server appears most likely because of an mDNSResponder cache problem. in order to get these inactive servers to once again disappear in OS X 10.3 or 10.4, follow the advice in the knowledge base article linked above. To make them disappear in OS X 10.5 Leopard, follow these instructions:
– Open the Network Preference Pane
– Select “Make Service Inactive” from menu at the bottom of interface list on the left hand side for the Airport interface and for the Ethernet interface.
– While the interfaces are inactive, relaunch the Finder (Hold down the option key, and click-and-hold the Dock Finder icon, until a menu appears with “Relaunch” as a menu item.
– Once the Finder is relaunched, make the Ethernet and Airport interfaces active again.
This should clear out the Bonjour cache of servers, and the Shared section should only list active servers once again.