Have you tried to install the printer as a network one? It would seem that on some Vista installs you have to set it up as a local printer even tho it really is a network printer.
The reason why you would get already is a port is because even tho you delete the printer that was using this port the port would remain by default.
My steps for doing a local port were done by going to Control Panel, Printers, Add a Printer then Add a Local Printer, Click Create a new port, leave the default local port, Click Next, a box will come up type in the actual address of the network printer, \\computername\printername - next will ask to install drivers, leave it shared and print a test page.
I am unable to print from a Vista basic machine. Here's my setup.
Computer 1: Running XP (that's the machine the printer is hooked up to.) Computer 2 running Vista premium I am able to print from this computer. Computer 3; Vista basic. This is my problem machine. I was able to get computer 2 to access the printer by "adding a local printer and assigning a port name. Worked just fine. Now I tried this on computer 3 and it did not work. It went through the process of adding a printer, but it would not print. I deleted the printer to try it again and this is when my troubles began. When I try to install a local printer, it says that port already exists. But the printer is deleted. I don't know how to work around this. I assume I need to delete the port, but I don't know how. Any help is appreciated. Thanks.