Chairman Ray said:
Just to expand form your last thread, the fan in the psu has to be facing the outside of the case. When cooling your psu, you want the air from outside your computer, not the air from inside, because the outside air is cooler. It doesn't matter if it's at the top of the case or the bottom, either way it should be facing outwards.
*Under ideal circumstances.
If the case doesn't have an air vent and only allows top mounting, then you can mount it at the top pulling air in, and it's perfectly acceptable to mount it at the bottom facing up, especially if the air intake would be stifled by carpet or something.
That being said, if your case is really bad, you can get a decent one for $40.