This depends on how the printer is shared on the network. There are different ways to share printers over a network. Among them are:
- Shared by Windows
If you're using Mac OS X 10.2 or later, you can use Samba printing. Open Print Center/Printer Setup Utility, and when adding a printer, hold the option key while choosing the different types of printer connectivity, and choose Windows Printing. You'll need to specify something like smb://<hostname>/<printername> at the very least.
Mac OS X Hints has a lot of tips on setting up Samba printers.
- Shared by a dedicated Print Server / Unix
Much more "reliable" to most people. Setup instructions are the same as above, but instead of choosing Windows printing, select IP Printing. You'll be asked for the printer type (LPD/LPR), printer's address (an IP address or domain name) and the name of the printer queue (which is the name of the printer; ask your Sysad).
There's Mac OS X's USB Printer Sharing and Rendezvous sharing as well, but I've not configured these yet so I don't know the step-by-step instructions.