I suggest you get more creative with your class build, going completely pure into one class isn't encouraged. If you haven't played before you should still have at least 3 class resets to try different builds.
Due to a recent DK un-nerf, I'm currently waiting for someone to make a DK Hybrid that doesn't involve additional mage or ninja levels.
You can view skill lists, and the classes here:
http://public.zodiacdev.com/index.php?title=Classes
Skill lists may be out of date (Warrior and Assassin for sure), so it's best to check the actual class trainer for a class before committing to a build.