After installing Data Bridge in the extension manager, when you open DW, it should launch the WebAssist installer to complete the installation.
it sounds like the WebAssist installer has not run.
Close DW, then open the extension manager. Remove Data Bridge, then install it again.
when you open DW, make sure the WebAssist installer runs to complete the install. if it does not run automatically, open a PHP page to force it to start. After the WebAssist installer completes, make sure to restart DW.
you may also want to delete the DW Cache file fro the users configuration folder: