This is an amazing way to improve your knowledge of a foreign language. When I started reading French novels, I could mostly understand maybe 60% and guess another 30%. But after 10,000 pages, I was only running into unknown words every few pages, and my understanding of idioms was vastly better.
The same thing works for listening comprehension: Find a DVD box set of easy TV series, one where you can understand maybe 40% of the dialog, and just start watching. It's OK to use a good dub of a series you've already watched. Repeat this with, say, 5 series and you'll see an amazing boost in listening comprehension. TV series are usually better than films for this exercise, because they'll give you 50+ hours of mostly the same people speaking about a limited set of topics, which helps a lot in the beginning.
It seems like the brain is very good at upgrading partial comprehension to nearly complete comprehension. But the trick is getting to an enjoyable level of partial comprehension.