To change the behaviour of the "Home" and "End" key in Mac OS X, which is "move the cursor to the top/end of the document" you should follow this hint which makes the keys behave like on most other operating systems (move the cursor to the beginning/end of the current line).
The page up/down keys can be "fixed" too.
In short:
Save this to Users/username/Library/KeyBindings/DefaultKeyBinding.dict

{

    "\UF729"  = "moveToBeginningOfLine:";

    "$\UF729" = "moveToBeginningOfLineAndModifySelection:";

    "\UF72B"  = "moveToEndOfLine:";

    "$\UF72B" = "moveToEndOfLineAndModifySelection:";

    "\UF72C"  = "pageUp:";

    "\UF72D"  = "pageDown:";

}