This should help get you started ->
http://www.watchguard.com/help/docs/v741WFSConfigurationGuide.pdfI would like to note that this product has been discontinued by the manufacturer, and I'm pretty sure that it's no longer receiving new fixes that "plug the holes" that have been discovered over time. -> If you don't mind getting your a little dirty, you might try loading m0n0wall onto it. The software is updated, and should help foil some attacks against this box. It's a unsupported modification however. ->
http://m0n0.ch/wall/tools/How%20to%20load%20m0n0wall%20onto%20a%20WatchGuard%20Firebox%20x500.pdf->
http://forum.m0n0.ch/index.php?topic=3073.msg12503;topicseen
