mysql_connect noob question

I know this has probably been answered already.

When I pass a user name and password from a form to my PHP script and 
then pass those to mysql_connect it doesn't connect. When I paste those 
exact same values into mysql_connect as string literals it works.

Can anyone tell me why this happens?

I know the strings are identical to the literals I try in a test but 
they don't work when submitted via form.

$form_user = $_POST[ 'user' ];
$form_pass = $_POST[ 'password' ];

# Connect to remote DB

$LINK = mysql_connect( $host, $form_user, $form_pass );

And yes, my $host param is correct.

Thanks,