Squash is similar to racquetball, except:
- the ball is dead
- the racquet is about the size of a badminton racquet (but sturdier)
- the lower 18" or so of the front wall is "out" which forces you to keep the ball up
- there are lines on the front, rear, and side walls that you can't hit the ball above
This site has a picture of the court:
http://www.us-squash.org/rules/csworld.html
There are some other differences, but these are the main ones. It's a physically demanding sport - especially if you're playing someone better than you. A better player can make you run your a$$ off.
I was wondering where ralpheb had disappeared to.