I always use the skew modifier to correct the perspective.
Just apply it to your camera, set skew axis to Y, enter 90 for direction, and fiddle with the amount to get rid of the 3rd prespective point.
No problems with Vray. (althought I had some problems with Brazil once..)
well the camera correction modifier in max6 works good.
it’s just annoying to use it. you always have to re-adjust it if you change the camera. and when switching to perspective mode the perspective is “corrected” too, and it’s a pain to reset it.
with finalrender there is a “architectual” camera type you can choose, and every render will be corrected automatically.