First of all you need to install the network driver. You can use the one that came with the router. When you install it, it complains that it is not meant for Vista, but install it anyways.
Now you need to install the printer driver for your specific printer. The problem is that Vista does not recognise the printer when it is attached to the USR8000.
What I did first is connect the printer directly via USB to the computer (In my case I had to use a USB to parallel converting cable).
After the printer is correctly recognised I installed the same printer as local printer. For the printer port I selected the USRPRTSHR port. You could probably also just change the port at which the USB-version of your printer is installed to USRPRTSHR.
Your printer however will not yet work unless it is at the default IP-adress of 192.168.123.254 . Under XP you would bring up the properties of the printer and select the <configure printer port> button. You would then be able to enter the correct IP-adress for your printer. Under Vista this does not work. Pressing the button will not bring up the window where you can enter the adress.
The driver stores the adress in the /Windows/win.ini file under the [SOHOmate] section. Vista does not use the win.ini file, except for program compatibility. You can edit the Vista version by hand. You might have to log in as administrator. When you have entered the correct IP-adress your printer should work.