The only thing that would come close to making trains economical in the US is a massive firebombing campaign of every city you hope they're going to run through, and even that would be pushing it, since even with cheap right-of-ways you'd still have to string them across the country.
See, in general, http://green.venturebeat.com/2008/04/11/why-the-california-h...
+ If you priced US high speed rail like Japan prices the shinkansen, it would cost you about $250 for a round-trip ticket from New York to Boston. I do the Nagoya to Tokyo circuit every once in a while for work. The system is one of the wonders of the modern world but, holy cow, is it expensive. (Its expensive to ride, its expensive to subsidize, and HOLY COW was it expensive to build. Shinkansen-related debt hit nearly 30 trillion yen -- that's in the general vicinity of $300 billion, folks. And that is for a country that would fit in California, with room to spare.)