Relevant information would be your existing network situation in addition to what you have tried so far. You said you have a wireless router, so I'll assume you're using it for an existing wireless network.
According to
the manual, using the installation CD that came with the printer is the easiest way to set it up with your existing network. Do you have the CD, and if so, have you tried it?
If you don't have it you can probably download it from Brother's website; you should have a utility you can launch at Macintosh HD / Library / Printers / Brother / Utilities / BRAdmin Light.jar, which you can use to administrate the printer's built-in server as desired (although you will need to somehow connect it to your network first; wired is probably easy than wireless initially, especially if the wireless is protected as it should be

).
To actually add the printer once it is properly networked, it should appear in the list of printers that are available to add in System Preferences | Print/Fax when you click the "+" button, if everything is configured correctly.
Again, I have the non-networked version of this printer, so I can't give you step-by-step instructions other than paraphrases of what I see in the manual, but hopefully this helps. If there's anything that's still confusing, I'd be happy to try some more.
