You can learn more than one dialect in South Korea. I'm from Suwon and I've lived in Gyeongju, and have stayed near Busan, Jeju island for months. Now I live in Daegu. (See where these cities are through http://maps.live.com/) When I'm in Seoul or in Gyeonggi province, I tend to speak standard Korean. When I'm in Busan or in any cities where are further south than Daegu, I tend to speak in heavier dialect than usual. It's funny. Actually Korean people in Seoul don't like others who speak the dialects very much because it sounds rough to them. So if you want to learn the dialects, you need to stay in the city that dialect speakers live. We don't speak North Korean which is ideologically quite different from Seoul Korean. You will hardly have many opportunities to use it, therefore learning it wouldn't benefit you in general. I'd suggest you to learn Pyeongyang Korean if you're going to be one of Kim Jeong-il's secret service men. :P To learn North Korean, you need to find any Korean people in Yenben or who defected from North Korea.