The end of the arm is covered by a very thin plastic cap that has to be pried off. It's so thin that it's hard to get something to grab it without catching the underside of the arm itself instead, so be patient. From there it's just a nut underneath and the arm comes off. You can then remove the rubber seal from the front of the cowl and pry the cowl off, it's just held in place by several plastic pins.
This should be pretty helpful:
http://www.rkrenn.com/xterra/mods/cb.../cbantenna.htm
See, I ain't all piss and vinegar. And FWIW, Schlud ain't all sugar and spice:
http://www.automotiveforums.com/vbul...d.php?t=170639