I contacted Brother on whether and when they would support MacOS X. Their official response via email was that they would not support beta OS's but would have drivers available soon after MacOS X is officially released out of beta.
You might not actually be getting to be root. Does you prompt change in terminal so that it says you are root? If not, try this example:
[localhost:~] malloroy% su - root
Notice how the prompt changed. You can also use this example:
The admin account is the account you created the first time MacOS X came up after the install. That account should have full admin privileges and supposedly is the same password for root.
At least, that is how it works for me. ;)
I have not tried that. It might work. The password for root is the same as the primary account (admin) you created when you installed MacOS X.
Alternatively, you can bring up a terminal window (in the Utilities directory of the Applications directory). At a prompt, type in su and hit enter...