Alright, after wrestling with this for a while, I finally pieced together enough information to get my Brother HL2070N working over the network for Xubuntu.
First off, you need to be able to manage cups on xubuntu. You have two options, re-enable the CUPS web interface, or install gnome-cups-manager:
For the Web Interface (blatantly ripped from here):
Select “System”->”Administration”->”Users and Groups” from the main menu on your desktop.
Select “Show all users” and/or “Show all groups”.
Add the user “cupsys” to the group “shadow” in the “groups” tab.
Restart cupsys by issuing the command:
$sudo /etc/init.d/cupsys restart
For gnome-cups-manager: (this will not install a menu item, you'll have to start this from the command line)
$sudo apt-get install gnome-cups-manager
If we wanted to use USB, we'd follow the steps here, but we want to use networking, so lets continue!
login to your CUPS web-config at http://localhost:631, or run gnome-cups-manager from the terminal.
Now tell CUPS that you have a network printer with IPP, with a URI of http:/aa.bb.cc.dd:631/ipp and that it should use the ESP HP LaserJet Series PCL 6 driver.
BAM, done. I tried for a VERY LONG time to get Brother's drivers working over the network, but since the 2070N has HP Emulation automatically, and HP Networks are included, this works perfectly!!!