Interfacing a 16x2 Character LCD to the Arduino
There are a few methods to do what you want to, and you will have to dedicate 4 or 8 pins to the LCD. Looking at the datasheet you provided, the LCD is driven by a HD44780, and this has been interfaced with Arduino many times - there is a subsection of the Arduino site's LCD page devoted to it (scroll down to find it). There are a few libraries that you can use - I would recommend Liquid Crystal as it provides both 4 and 8-bit modes, and apparently comes with the Arduino software. You probably could reuse the pins though by making use of enable/chipselect pins and then attaching boards/shields on top. This question may assist with that.