Our company's Windows network requires periodic password changes, and each time I do this (via a Windows machine, BTW, since I don't know how to do this from a Mac), all my Windows networked printers break. One solution is to delete the printers from Printer Setup Utility and then re-add them, but this gets old fast, especially if you have several networked printers.
The easiest method I've found is to first change the passwords directly, and then restart PrintingServices. The passwords are stored in a root-owned file at /etc » cups » printers.conf, in a URL for each printer:
DeviceURI smb://USERNAME:password@Workgroup/path/to/printer
You can easily edit this file in Terminal.app with sudo vi /etc/cups/printers.conf (Type :1:$s/old_pword/new_pword to change them all at once!). Save the file, then restart CUPS: sudo SystemStarter restart PrintingServices.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070329163756674