You will still need to install the deprecated server behaviors extension. You should be able to do that from the Adobe Exchange by using the Dreamweaver menu item Window->Browse Add-ons...
To install webassist extensions the best option is to use a third party extension manager since Adobe dropped support for the Adobe Extension Manager. DMXZone offers a free alternative:
http://www.dmxzone.com/go/22670/dmxzone-extension-manager-for-dreamweaver/