The file KeyEventTranslations.tr which can be found in the directory $InstallationDirectory/SystemFiles/FrontEnd/TextResources/Macintosh couples key events to actions in Mathematica. The two lines that define the behaviour of Home and End are
Item[KeyEvent["Home"], "ScrollNotebookStart"],
Item[KeyEvent["End"], "ScrollNotebookEnd"],
To change the behaviour of these two keys you could replace "ScrollNotebookStart" and "ScrollNotebookEnd" to "MoveLineBeginning" and "MoveLineEnd", respectively.
To be on the safe side, you could copy the file to the directory $UserBaseDirectory/SystemFiles/FrontEnd/TextResources/Macintosh first and edit that file instead of the original in $InstallationDirectory.
tutorial/MathematicaFileOrganizationin the Documentation Center but that's about it AFAIK. – Heike Apr 10 '12 at 09:59KeyEventTranslations.trin$UserBaseDirectory/.../Macintoshwasn't picked up on my system. I'll continue to poke at it and see if I can figure out where I should put it, but in the meantime, if you come up with something, please post an update. – rcollyer Apr 10 '12 at 15:16