Q5.0.12: How do I disable gnuserv from opening a new frame?

If you set the gnuserv-frame variable to the frame that should be used to display buffers that are pulled up, a new frame will not be created. For example, you could put

(setq gnuserv-frame (selected-frame))

early on in your init.el, to ensure that the first frame created is the one used for your gnuserv buffers.

There is an option to set the gnuserv target to the current frame. See Options->Display->"Other Window" Location->Make Current Frame Gnuserv Target

You can also change this with Customize. Select from the Options menu Advanced (Customize)->Emacs->Environment->Gnuserv->Gnuserv Frame... or type M-x customize RET gnuserv RET.