The exact steps will vary a little depending on which version of the MacOS you're using, but generally speaking Brother's networked printers have Bonjour on by default, so should be pretty easy.
Basically, go to the "Add printer" thing (either in the Preference Pane on fax and printing, or Printer Setup Utility in the Utilities folder, depending on OS version), select "Add printer" (again, either the + button or "Add" in the toolbar), and under the Default Browser your printer should just appear (it'll have an odd name, though) if it's on the same subnet as your Mac.
Select it, pick the correct driver, and you should be good to go.
If it's not showing up, you may either need to enable Bonjour or add it manually, but a little more info on your setup would help to give tips on that.