Open a notepad.
Paste this.
<title>YOUR SITE NAME HERE</title>
<body bgcolor="#000000">
<div align="center">
<p>
<a href="news.php"><img src="YOUR PICTURE NAME HERE.jpg" alt="" border="0" />
</a>
</p>
</div>
</body>
</html>
Save as filenamehere.html
Now, this is exactly copied, pasted, and everything fate related from the source of the page you linked, but should work for you. Long story short you need some sort of html knowledge to make the splash page, and this will do it provided you replace the YOUR PICTURE NAME HERE.jpg with a link to the picture you want to display, and YOUR SITE NAME HERE with a name you want so that phrase isn't at the top of your browser window.
Now upload it to your site, and copy that path to the box in the admin splash page link provided by the previous attempt to help.