Some people who have installed Snow Leopard have found that their printer is not functioning properly, if at all. Many times the printer appears to have been uninstalled after updating.
Changes in the printing system between Leopard and Snow Leopard may have the operating system reset the printing system upon updating, which will remove all printer devices, so the printers need to be added again. In order to add your printer back to your system, be sure it is on and plugged in (or on the local network) and then follow the instructions in this knowledgebase document: http://support.apple.com/kb/HT3771
Another issue might be the lack of installed drivers for your printer. Apple set Snow Leopard to install only the drivers for "nearby printers" by default, which might not have happened if the printer was not recognized by the system. This may be particularly true for networked printers.
To install the printer driver on your system, first check Apple's knowledgebase document on supported printers to see if your make and model are supported. This document can be found here: http://support.apple.com/kb/HT3669
If your printer is listed, insert the Snow Leopard DVD and launch the "Optional Installs" package in the "Optional Installs" folder. Agree to the license, select your hard drive as the destination, and then check the "All Available Printers" option under the "Printer Support" category. This should install the full gamut of printers available in Snow Leopard, instead of only installing the default limited number of printers. The install will take up about 1.3GB of space, though this increase should only be about 350MB more than the default set of printer drivers.
Topher has been an avid Mac user for the past 10-15 years, and has been a contributing author to MacFixIt for just over a year now. One of his diehard passions has been troubleshooting Mac problems and making the best use of Macs and Apple hardware both for family and friends, as well as in the workplace. He and the newly formed MacFixIt team are hoping to bring enhanced and more personable content to our readers, and keep the MacFixIt community going here at CNET. If you have questions or comments for Topher or the other MacFixIt editors, feel free to contact us at http://www.macfixit.com/contactResources