generally those kinds of translators can be o.k. if you are looking up a single word, but are awful if you are trying to translate anything more than that.  even with single words, they can be inaccurate..  
the best (in my opinion) korean/english online dictionary is at 
http://endic.naver.com/ - you can search in korean or english, but again, it's only good for looking up single words, and even then, take everything with a grain of salt.  
unfortunately, there really isn't a way to translate without understanding the language or asking a person who does understand the language.  if you have more questions, there are plenty of us here who can help (: