ok, then let's check some more:
usbfs in /etc/fstab, check ?
permissions of /dev/usb/lp*, check ? (crw-rw---- 1 root lp 180, 0 2008-01-27 10:29 /dev/usb/lp0)
well, have a look at the gentoo-wiki.com, if there's more tips to this "problem, check ?
search for brother printer cups ubuntu @ google ...