Total N00b question about Cpu cooler.

I noticed somethign odd and I'd like some feedback. I replaced my stock heatsink on my p4 2.6ghz cpu with the 90cm copper zalman cooler and I have noticed a difference in temps. But heres the problem. I noticed when I was cleaning out the case the other day that the fan on the sink was blowing air downwards. In other words when i put my hand over it i did not feel it blowing.

I then said to myself "self. Which way is this thing SUPPOSED to blow?" So thats what I am asking. Is the cooler supposed to blow downards or upwards. If it is going backwards could this be a wiring fault of the mobo? I remember noticing something similar on the stock HSF when I first installed the chip but i passed it off as nothing.

I am ashamed to sound like such a nublet but it would be a shame if I had installed AS5 and a nice new zalman HSF only to not get optimal cooling on the cpu.

thanks.

Virtually all fans blow downwards.

Some blow sideways and out the back of the case.

Almost none blow upwards.