Apple has introduced a new feature in OS X Lion which is known to be as ‘natural’ scrolling. Previously you would have moved your finger down to move down, and up move up on your mouse/trackpad, where as in new ‘natural’ scrolling the process is reverse.
The new feature seems to be difficult for some users. The new feature can be disabled in the settings so that the previous scrolling can be used.
Goto System Preference > Mouse > then remove the tick from “Scroll direction: natural” or “Move content in the direction of finger movement when scrolling or navigating”
Now the scrolling will be in reverse.