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