Former Texas resident here:
True, Dallas and Houston are large, and the countryside between them poses few engineering challenges. And true, HSR has failed so far. But several things are different down there.
First, both cities have "secondary" airports available with abundant gate space. Not so with NYC, or with many other cities in the northeast. Herb Kelleher, the president of Southwest Airlines, has pointed out that he could easily expand the number of flights from Hobby to Love Field, something that no one could say in our corner of the country.
Second, the area between those two cities is not very heavily populated. And the intermiediate cities are where HSR will get its best market share--places that are big enough to support a station, but which have crappy or nonexistent air service.
Both cities are also decades behind the rest of the US in terms of planning for (or even thinking about) growth. Neither city had functional light rail until a few years ago, and getting it built was a serious struggle. Both cities sprawl out on a scale not seen in the northeast, and the overall attitude toward planning is openly hostile. Sprawl just isn't seen as a big issue--sure, the city spreads out and gobbles up more and more land, but so what? Land is abundant. It's not like there are beautiful, scenic areas being spoiled with strip malls. The Houston-Dallas corridor didn't have anything beautiful to look at to begin with.
Texas being Republican doesn't help at all. The Texas congressional delegation has several prominent members who are outspoken (read that "rabid") opponents of ANY form of mass transit as a matter of principle. Tom Delay basically thinks any public investment in a system like that is tantamount to communism. Think I'm exaggerating? Listen to him on the subject of the Houston light rail system, which actually serves his district. It's like listening to the John Birch Society talk about fluoridating water back in the 50s. And he's not just an isolated nut-case, either. (He's not isolated, that is...)
That said, Albany-Buffalo is, IMHO, not a good candidate for dedicated high speed rail on the European or Japanese model. The population density isn't there, and what population there is, is declining.
The one good thing about the route would be the abundance of routing options--NY state owns an interstate highway, a canal, and large portions of an abandoned RR ROW, which could be used in concert with one another to lay out the line. Certainly, a large portion would end up in the Thruway median, or above it on piers. Combine that with an existing ROW that was built for four tracks and currently houses two, and you certainly have a head start on right of way acquisition.
Honestly, I think the best places in the US for a dedicated high speed rail system would be Florida (flat, lots of tourists who don't want to drive and lots of old people who shouldn't) and Ohio (flat, lots of medium sized cities spaced at distances that HSR is ideal for). But it will probably happen first in California.
