As we do here in Canada with 2wd pickups (2wd Xterra was never sold here)... keep a lots of heavy stuff in the back (4 bags of 40 pounds of sand are good, you can use the sand as an abrasive if your stuck on some icy roads).

Studded tires are less expansive than hi-end winter tire. they are noisy on the pavement but very gripping on ice.