Need help Snow javascript plugin

First of all I want to say Hi to everyone,
I’m new to this forum and work for the first time with wordpress.

I have a problem with my wordpress I want to include the following plugin to my website:
http://www.schillmania.com/projects/snowstorm/snowstormv13_20081215.zip

just a snowstorm.js and the images for the snow.
the snow is visible so you might think it works but the problem is that my RSS isnt working anymore.
This is my site:
http://www.leodag.nl/blog

I includes the script in the index.php this is my index.php:

<script type="text/javascript" src="christmas/snowstorm.js"></script>
<?php
/**
 * Front to the WordPress application. This file doesn't do anything, but loads
 * wp-blog-header.php which does and tells WordPress to load the theme.
 *
 * @package WordPress
 */

/**
 * Tells WordPress to load the WordPress theme and output it.
 *
 * @var bool
 */
define('WP_USE_THEMES', true);

/** Loads the WordPress Environment and Template */
require('./wp-blog-header.php');
?>

as you can see I’ve used <script type=”text/javascript” src=”christmas/snowstorm.js”></script> to load the snowstorm script.

this is what I get when I go to the rss page http://www.leodag.nl/blog/?feed=rss :
Warning: Cannot modify header information – headers already sent by (output started at /home/leodag/domains/leodag.nl/public_html/blog/index.php:4) in /home/leodag/domains/leodag.nl/public_html/blog/wp-includes/feed-rss.php on line 8

What did I do wrong?
Thanks in advance