Just use the addslashes function it will escape any characters that need them.
$message=addslashes($message);
if someone sends the message
"some message" is here... ' here is another'
then after going though addslashes the message will be.
\"some message\" is here... \' here is another\'
when you send this using your email routine it will drop the slashes and send the message in its original form.
Mark.