System Preferences > Language and Text > then click on the tab at the top that says "Input sources" and find Hangul, click on it.
then go to System Preferences > Keyboard
Find the box under "keyboard" that says "Show Keyboard & Character Viewers in Menu Bar" and make sure the box is checked.
then at the top right in ur menu bar, u shud see a little american flag. click on it, and there shud be a scroll-down menu that includes Korean in it. if this doesn't work, then just ask, cuz my directions may not have been clear; sorry if they werent hahaha