JOEL - Here are the relative scriptures:

"And he(Noah) drank of the wine, and was drunken; and he was uncovered within his tent.
And Ham, the father of Canaan, saw the nakedness of his father, and told his two brethren without.
And Shem and Japheth took a garment, and laid it upon both their shoulders, and went backward, and covered the nakedness of their father; and their faces were backward, and they saw not their father’s nakedness. And Noah awoke from his wine, and knew what his younger son had done unto him.
And he said, Cursed be Canaan; a servant of servants shall he be unto his brethren." (Gen 9:21-24)

Ham's brothers walked in backwards, because it was considered very disrespectful and against the laws for the children to see their father unclothed.(See Lev. 18:7, 9)
People have speculated for centuries about why Canaan was cursed for Ham's offense in these scriptures. Some say that the editors of Genesis made a mistake and put Ham in the place of Canaan, and the Book of Jubilees says that Ham was outraged at the injustice to Canaan (Jubilees 167:7, 13).
Man is punished for his own sins, but punishment for our unrepented sins isn't really supposed to happen until after we are judged by God in the next life, although we may suffer some natural consequences for our sins in this life.
A curse on the other hand is something that usually is in effect only during mortal life. And often God's "curses" are not intended as punishment, but are meant for the sake of improving the person cursed, even though the immediate consequence may be extremely unpleasant.
It is possible that Noah may have perceived that Ham's irreverent behavior was also already evident in his son Cannaan, which may be why he singled out Canaan as he imposed the curse.
It is also possible that rather than being a punishment, the curse may have been more like a prophecy of what Noah saw would happen to the decendants of Ham.
Curses can have an effect on future generations as in the case with Adam. We are not punished for Adam's transgression but we do suffer the effects of what God did to him when he fell. God "cursed" the ground for Adam's sake(Gen. 3:17), but the effects of the curse continued on to everyone of Adams decendants, including me and my weed infested garden.