need to remove newline characters from form input

I'm writing a simple threaded message board using only php. I have it worked out except for having to make sure the user input from a <TEXTAREA> doesn't have new line characters. I need to add those myself. Is there an easy way, short of checking each character in a loop, to rid input of new line characters. Also, ( this might come in handy lol ) what new line character is created when the user presses the Enter key when filling a form field? If they aren't " \n" I'm not sure what Im looking for. much advance thanks, Dale