If you want to use two or more computers at the same time you have to use the render animation command. I have done a few network renders, but only between two computers. Click on the bottom Setup button to open another window. There are three buttons at the bottom. "Save client list" can't be used until you "update" and find all the computers on your network. These have to be on and running bryce lightning and not firewalled in order to be found. The next button "use host to render" allows the main computer to also render. This command was removed in 5.5 so if you have the latest bryce you have no choice. The last button "use tile optimization" allows each computer to do a block of the total picture. This is what you want because you are only doing a single frame. If you don't check this one computer will get the entire image and it's like you just rendered to disk anyway.

I've run both big singles and animations this way. Whenever a computer gets through with a block it asks for the next one. These started at the top left and went to the bottom right on the screen. My lightning machine ran about twice as fast as the host. You could see it finish one block and go on to the next one on the screen. The host most of the time jumped over the two blocks that the lightning machine had and started the next. When I hit a patch with glass or reflections it took longer to render than bare sky. It really depended on what type of object and material was in that tile as to how long each machine took.