There is no reason why installing the printer as a "Network Printer" in Vista should have any effect on the other PCs' printer configurations.
However getting the printer installed in Vista can be problematical. Follow these instructions:
In the Vista "client" PC, launch the "Add a Printer" wizard and select the "Add a local printer" option. This automatically opens a new dialog box in which to select the Port.
Click the "Create a new port" radio button and leave the drop-down menu options on the default of "Local Port". Click Next.
A small box opens in which to enter the Port Name. Type in the path to the "shared" printer in the host PC using the format \\computername\sharename.
Select the Printer driver from the list provided, which should include the driver