Apple has released updated sets of Snow Leopard drivers for Hewlett-Packard and Epson printers and scanners.
First on the line is version 2.4 of the Epson drivers, which comes in a package listed on Apple's download page at a whopping 737MB; Epson Printer Drivers 2.4 provides updated compatibility between Mac OS X 10.6 or later and dozens of scanners and printers made by the manufacturer.
On the HP side, the update, dubbed version number 2.4.1, is listed at a significantly smaller 388MB. (Note that actual update sizes vary, depending on the specific drivers you need.) HP Printer Drivers 2.4.1 requires OS X 10.6.1 or higher in order to function and provides support for both printers and scanners made by Hewlett-Packard.
Both updates can be installed through Software Update, or obtained directly from Apple's Website for Support Downloads.