What might actually be meant, is there are programs that can take a sentence (or series of sentences) and correctly categorise them, enter them into a knowledge base, although the program doesn actually comprehend/understand the sentences.
It has for a long time, and still is, a large problem trying to create good translators that can correctly (fluently) translate one language into another. The problem is that to do this does require an understanding of the passage being translated. Actually understanding a language requires an ability to grasp the context of what is being said, which computers currently have difficulty doing. A good example (although many years old) in AI: A Modern Approach is (page 21), the english to russian (or russian to english?) translation: "the spirit is willing but the flesh is weak" was translated as "the vodka is good but the meat is rotten".

Yeah sorry, by understand I ment they could break the new sentence into a series of statments and add these new fact to the KB, as opposed to actually understanding how to carry out a conversation.

I''m really thinking that ThoughtTreasure has the best approach so far that is reasonably well explained. It seems to use some logic processing as well as a natural language parser to get the knowledge back out of their KB. Although it is quite limited in its communication abilities, they''ve got what seems to be a great approach to storing different forms of knowledge. I''m especially impressed with how they''ve managed to get their conventional KB to interact with maps that have been defined and to find paths through them to attain goals. As well they have implemented scripting, allowing the application to understand more complex sequences of actions, like buying an airline ticket. I''ve got high hopes for their project...