This crappy site wouldn't let me add some info on the specific episode, number 51, so i am posting here.
I was watching Urusei Yatsura number 51 " There's a Cat on the Stairs" and the I recognized the song they played right after the intro, but couldn't place it right away. It's the Beatles' "Fool on a Hill." They start the tune halfway through the chorus, but I just thought it was cool that they played it, and hoped that if I post something about it that someone who can't place it in the future will find this post. I also wonder if there was some importance to their choice of song. Let's see if there's a response in about 3 years from now!