Can I an RS422 interface to Arduino's serial pins?
You need to interface the RS422 properly to the Arduino.  There are special chips that do this for you.  Just like you would use a MAX232 (or similar) to interface the Arduino to an RS232 system, you need to shift the voltages to the right levels, and create or combine the differential pairs.

Maxim (the makers of the MAX232 chip) make a number of chips for RS485 and RS422 systems. Their parametric search shows them all: http://para.maximintegrated.com/en/search.mvp?fam=rs485&amp;hs=1

Other companies make chips that do the same job as well.