Can you put the page you want into a new sub directory? If so, use htaccess.
http://www.javascriptkit.com/howto/htaccess3.shtml
If you use a field, then you would have to use javascript, perl or php to make read the password field.
In php, it would look something like this:
If the password field has a name of password and the password is "test1234", then when variable is passed to the next page, the php code would...
$variable = $password;
PHP Code:
if ($variable == 'test1234') {
echo "that is the correct password.";
} else {
echo "Sorry, you loose!";
}
Dave