First off, Snow Leopard no longer supports AppleTalk. If your printer was connected to your Mac via AppleTalk (which was the case for me), the printer won't respond after upgrading to Snow Leopard. To get it working again, go to the Print & Fax System Preferences pane and click the plus (+) icon. This brings up the Add Printer window. Confirming the lack of AppleTalk support, the toolbar no longer includes an AppleTalk icon/button.
If the name of your printer appears in the Default list, select the name and click to add it. All will likely be well. However, chances are good that a previously AppleTalk-connected printer is too old to include Bonjour support and thus won't show up in the Default list. In this case, you'll need to do a bit more work to add the printer back.
While you can no longer use AppleTalk, most of these old networkable printers also support connecting via an IP protocol. If not, you may be completely out-of-luck; the possibility looms that you will need to buy a new printer. Hopefully, it won't come to that.
To attempt to add the printer via IP, click the IP icon in Add Printer's toolbar. What to do next varies a bit depending upon your printer model. In the case of my HP LaserJet, I followed the advice on this . In particular:
1. Click the IP button and select HP Jetdirect - Socket from the Protocol pull-down menu.
2. Enter the printer's IP address in the Address text box. Don't know what the address is? Not to worry. Print out a Configuration Page. For my 4000N, I used the Menu and Item buttons on the printer to get Print Configuration to appear in the LCD screen; then I hit Select. On the resulting printout, I located the line that said IP ADDRESS.
3.
If things go well, shortly after entering the IP address, the Print Using line at the bottom of the window will list the name of your printer (as seen on the right). If so, click the Add button and you are done. Your printer should be ready to work with Snow Leopard.
If you have another brand of printer, you'll likely need to choose Internet Printing Protocol - IPP instead of HP Jetdirect. And there will be a different means to determine the IP address. But the basic procedure remains the same.
One bit of good news: You shouldn't have to install any new printer driver software. The latest versions are already installed via the Snow Leopard upgrade.
Unfortunately, this was not the end of the story for me. After following the above steps, the name of my printer did not appear in the Print Using line. Instead, it said Generic PostScript Printer. I went with this choice, hoping that it would work, but had no success. The printer was added but I still could not print to it. I tried again with other possible Print Using choices, as obtained via the Select Printer Software option in the pulldown menu. Nothing worked.
Contacting HP for help was useless. The company told me that it no longer offered support for the 4000N. An . Another Apple article provided . But neither article pointed the way to a solution.
Undeterred, I searched the Web and eventually found an HP Web page that described the procedure for : Turn the printer on while holding down the Go button. (If you try this, don't remove the printer's JetDirect card, despite what the Web page says.) The reset forced the printer to update its IP address, to one that now matched my current local network. I entered this new address in the Add Printer window. Success! I am once again able to print to my still trusty LaserJet.
I also have a Canon inkjet printer, connected to my Mac via the USB port on my AirPort Extreme. Prior to Snow Leopard, I could not directly access the printer's options to check its ink levels--as Leopard did not permit accessing this feature from an AirPort-connected printer. To do so, I had to temporarily connect the printer to a USB port on my Mac (or use the information available from the LCD screen of the printer).
In one of Snow Leopard's less-publicized improvements, this situation has changed--for the better. If your printer's ink levels are low, a low ink warning now appears in the Print dialog--even with an AirPort-connected printer. If you click the warning icon, a display appears that shows the current levels of each individual cartridge. Cool.