Many Brother printers are not easy to get working in Gentoo and Sabayon Linux (see, e.g. Re: Can I install .rpm or .deb drivers on Sabayon?
). There are third-party Gutenprint drivers for some Brother printers, but not the model you have. However, there is a Gutenprint driver for the Canon Pixma MX870 (see Gutenprint Supported Printers
), so you can get that printer working. Install the gutenprint package from the Entropy repository if you have not done so already.
As with many distributions, the best way to manage printers is to use the CUPS browser interface. Launch a Web browser and enter http://localhost:631/
into the Address bar in order to use the CUPS manager. Use CUPS to install the printer.