You can also install Bonjour for Windows and have the printer show up in the Default ("easy") list.
When you read the write-up in the Apple Help, it covers all sorts of processes in adding a printer in Mountain Lion. It does tell you that there is an option that you can add a printer to use on the network, which is plugged into either a print server or a non Mac PC on the LAN network. what it does not tell you is how!
I struggled to do so and thought to see if I can add a little light.
Open System Preferences / Print and Scan / and click the + under the list of installed printers.
a Window appears with "Add" on top and four types of printers appear. Default handles the easy ones that Mountain Lion can see. Fax is for that, and you are left with IP ( for tricky printers plugged into your router or switch directly. You can use Gutenprint drivers if you need to down that route. The last one is The one we are looking for- The Windows icon. Click it and you should see your network appear with its name below. Click it and a list of Pcs/devices on the network will appear. select the PC your printer is plugged into and your printer you want should appear. Select that and the printer listed should appear below in the top horizontal white bar of three below. Location will probably stay blank. If the software is readily in the system you select that and it should easily become listed to install.
If the Printer is not in the system you have a problem in the lower line called Use. select the little arrows on the right of the box below and you get some more options: Choose a printer or diver model will be greyed out, along with Auto Select. You can select a Generic Post Script Printer if you have no other choice with that type of printer or a Generic PCL Printer if that is what you have. I used this for a Photocopier is have and it works.
If you need to use a regular printer which is not appearing you can choose either "select printer software" or "Other".
"Select printer software" can be selected and when I did it I ended up with a block with blank horizontal blue and white stripes. No other info.
When I selected "Other" I could search for drivers in the Mac but I found none. The Guy I called at Apple South Africa showed me a neat trick.
Right Click on the main task bar next to "Add" on the small block mentioned above and the drop down menu appears with "cusomise toolbar" on it. Look for the icon "advanced" and drag it near the word "Add". Select Advanced when it appears on the taskbar.
It will immediately actively search for printers properly, as well as detect your type of network. Select LPD/LPR Host or Printer
Ignore "Another device"
You can add the printer as it appears on the network in the line URL: lpd://BobsPC/Networkprintername
the exact name as it is set for sharing in Windows network is important here.
I tried this and it worked well.
I did however go into the Print server where the printer was plugged in and simplified the name of the printer to a short name.
the MAC will also ask for authorisation and ask for the administrator user name and password of the printer's home PC. My Printers PC did not have one in the User profiles listed so I went and gave it a simple one and then the Mac allowed me to access it.
When I did this the printers were actively searched and I selected the correct one that Apple said they had a Mountain Lion Driver for.
It saw the printer.
I then went back to the Select printer software option listed above and the Block with empty white and blue stripes was now populated with the full list of compatible printers. I selected the correct one and from then on it was simple to get the printer working
I hope this helps someone.