Megan McArdle is right; this alleged quotation from Marx's Capital supposedly "making the rounds on Wall Street" --
Owners of capital will stimulate the working class to buy more and more of expensive goods, houses and technology, pushing them to take more and more expensive credits, until their debt becomes unbearable. The unpaid debt will lead to bankruptcy of banks, which will have to be nationalised, and the State will have to take the road which will eventually lead to communism.-- definitely is not Marx. It sounds more like a half-informed graduate student summarizing what he thinks Marx might have said about the current recession, and besides, "taking the communist road" sounds more like Maoist lingo. (If it really was from Capital, you'd more likely see a tedious reference to how much wool could be spun from so many spindles and so forth.)
Not that nothing in Capital is relevant to the current situation. Marx does have a few sketchy pronouncements about the credit system and about potential effective demand problems -- the need to discipline the ways in which the working class reproduces its labor power and get them to soak up some of the surplus and so on. I think the passage I quoted in this post, from the chapter on money in volume one, has some application, for instance.
But the idea that Marx suggested that the state would lead a country down the path to socialism is absurd; generally the state is regarded as being completely captured by the capitalist classes to do its bidding. Or else capitalists have ceded political power to the state so that it can divide the working class's wrath between Business and Government. Or else the state operates as a competing power base in a triangulated struggle over the shape of social relations. Etc., etc. But the general gist of Marx's theory is that a revolution is necessary to smash the state and eventually do away with it.
Whoever made this statement up and attributed it to Marx probably wanted to use Marx as a kind of boogeyman, who is supposed to automatically discredit any idea that he can be associated with. The gambit here is to discredit the Fed and Treasury's efforts to ameliorate the financial crisis and make sure nationalization remains a dirty word, as Yglesias talks about here.