You will need a flat subfloor. I laid 1/4" luan over mine as the CDX was pretty rough. Then you put a black plastic vapor barrier down. I used a pneumatic stapler for this (not the same as a pneumatic FLOOR stapler), as the plastic slides around and the stapler lets you reallly fasten it down quickly and easily.
It took me 2.5 days to lay the hardwood floor (all the prep time - luan, etc.. was extra time) - had a lot of trim work. Oh yeah, a power miter saw helps a lot to get good, square clean cuts on the ends of your boards, if they are going to show, as in a doorway/entry to carpet or some other floor.
good luck. It's a lot of work, but very satisfying when the job is done.