<< I don't want to tamper with it and leave our network open to bad people. >>
As Phil D has confirmed -- unplug your cable connecting the internet side of the router to the "modem".
I'll drop out now since you have two offers of help from people and as I've said I'm not strong on network problems -- I guess I'm lucky <s>
I'm still a little concerned at the term you use "Private Network" -- I usually refer to what I have as a LAN -- Local Area Network -- and I'm afraid that the Private Network you have set up might be something so secure that it defeats what you want to do!
I very strongly recommend that you stop trying to troubleshoot what you have now and go back to two independent machines by deleting the network you have and starting again with the Network Wizard -- it asks you some simple questions like does (the computer you are working on) connect directly to the internet or through a "gateway" such as another computer (server) or a router and it shows you very clear illustrative maps of what they are talking about.
You should end up back in a similar situation to the one you are in at present but without barriers and able to Add Printer on the PC that does not have the printer directly connected to it.
I'm in XP at the moment and VISTA does differ but I've just looked up "Private Network" in HELP and it does not seem to be the same network diagram as in a LAN. In the Private Network one PC has two Network Interconnection Cards one of which goes to the Internet and the other goes to a network hub to which other computers are connected. Your physical setup as you describe it (and mine) has none of the computers directly connected to the internet but all of them connected to the router which connects to the modem that connects to the network. I doubt that VISTA is different in this respect.
I suggest you look up "Network Setup Wizard" in your VISTA HELP and see what it says which includes, in XP, the following:
If you select This computer connects to the Internet through a residential gateway or through another computer on my network on the Select a connection method page, the Network Setup Wizard will open the Windows Firewall ports needed to discover a residential gateway and ensure that Internet Gateway Device Discovery and Control is running.
which would seem to deal with the question of the right ports being open.
Sometimes the best thing you can do is to start all over again!
You live in a nice part of the world -- I live in Florida now but spent a lot of time in the Carolinas, mostly based in the Greenville-Spartanburg area because of the textile industry so not far south of Charlotte. <s>
Message Edited by huwyngr on 07-15-2008 11:48 AM