How can I remove old SMB connections?
It depends on how this was set up to launch.  From boot, Go > Connect to Server > (click the dropbox) and select clear recent servers, if not using any.  Then go to System Preferences > Accounts and see if there is something set up in the Login Items tab related to the server and clear.  Restart and test.  If it continues I'd check Macintosh HD > Library > LaunchDaemons for a file related to mounting the server.