I have only read the first book but the TV series seems to take Catelyn in a somewhat different direction in the end. Maybe I missed something in the book or maybe it will come in season 2 of the series, but was Catelyn's "We will kill them all" line to Robb added? In the end of book 1, she tries to push for peace. In the book, she also recognises her error in trying to seize Tyrion and precipitating war. I don't recall her almost braining Jaime with a rock either.

I think Catelyn's a rather interesting character regardless - a good person who makes some bad choices and is constrained by her honour, rather like her husband. It was quite an unusual plot mechanic that she would cause things to go to hell by her action in seizing Tyrion. Typically, in stories, it's the evil people who precipitate the chaos. (Although no doubt things would have turned bad sooner or later regardless, with Ned's investigation into House Baratheon and the poisonous nature of the Lannisters.)