Be careful which pins you use. P1_2 is the RX pin for Serial. Since you call Serial after you instantiate the Keypad things will get messed up and could be the reason why things don't work.
I also read through the Keypad code from http://www.pjrc.com/teensy/td_libs_Keypad.html and see nothing in this code that would not work on MSP430. Of course the devil is in the details but at first glance this should just work.
Try a different pin than P1_2. You can find the pin map for the MSP430G launchpad here: http://energia.nu/Guide_MSP430LaunchPad.html