Your wish is quite reasonable. I don't like the Cmd left/right arrow too.
You can often use Ctrl-A to go to the start of a line and Ctrl-E to go to the end of line.
First of all, have a look at this web page by Jacob Rus:
http://www.hcs.harvard.edu/~jrus/site/cocoa-text.html
A good explanation of key related things.
In your personal Library folder create a folder KeyBindings.
Then copy the following (starting on the line with { and ending on the line with }).
(this will also make Shift Home and Shift End select to the start/end of line)
{
/* home */
"\UF729" = "moveToBeginningOfLine:";
"$\UF729" = "moveToBeginningOfLineAndModifySelection:";
/* end */
"\UF72B" = "moveToEndOfLine:";
"$\UF72B" = "moveToEndOfLineAndModifySelection:";
}
Paste this as PLAIN TEXT in an empty file in your favorite text editor (Smultron?) and save the file as
~/Library/KeyBindings/DefaultKeyBinding.dict
(NB: use Unix line endings)
(NB. You can do much more with keybindings
Logout and login again and you should have what you want.
This will work in most applications using the Cocoa text system.
But not in some: Safari in the address field and in the Google search box; you have to use Ctrl-A and Ctrl-E.
Berend