The DMXZone Extension Manager works well with our stuff and should be used for installing our .zxp files.
It is their version of the Database connectivity and Server Behaviors that we don't work with. You can install the Adobe version from the Adobe Plugins page. From Dreamweaver go to: Window->Browse Add Ons... that will open a browser window. Then click to sort by "most popular" and the Server Behavior and Database extension will be the second one. You can install it directly from there.