You do not have to manually create a new port and i have attached shared and nwetworked printers with or without UAC. I currently have UAC turned off - its soooo much more pleasant to interact with the system that way.
As long as the XP SP3 printer is shared and Vista SP1 file sharing, private network location and network discovery is turned on - you're good to go.
1. Click on "Printers" from the "Start" menu of the Vista machine.
2. Click on "Add a printer" from the "Printers" window.
3. Click on "Add a network, wireless or Bluetooth printer" from the "Add Printer" window.
4. The "Add Printer" window will start searching for shared, networked or wireless printers.
5. Select the shared printer from the "Select a printer..." list in the "Add Printer" window.
6. Done!
I've done this many times.
P.S.
Sometimes, with XP or Vista, network/shared devices may not appear right away. You can try and manually initiate a new search for devices or just let the system stand for a while or reboot. In any case, in my experience, if the network or shared devices don't show up right away, go get a cup of coffee, they will show up eventually.