The OS X Print Center already knows about LPR printers.
- Start up Print Center (it's in Applications/Utilities
- Click on Add
- Select IP Printing from the pull-down list (if it's not already selected)
- Type in the host name or IP address for the printer.
- Uncheck 'Use default queue on printer'
- Type in a queue name (You can type anything here, make it easy to remember)
- Select the printer model
- Click on Add.
That should do it.