On several occasions, I have attempted to create rollovers using JavaScript. When previewed through Dreamweaver (Browsers IE and Netscape), the scripts work great, but when I post them to my server, I get "variables navc and navcover, undefined". Note, I didn't use the Dreamweaver scripting tools; I am trying to create my own code, using several different scripts I found in Javascript manuals. I I can't figure out what is happening after I load it on my server. My host says the server should make no difference because it's a client-side script. Okay so??
Please, some advice.

In the following example, I am using the same original and rollover images for all of my links.

<html>
<head>
<script language="JavaScript">
<!--
if (document.images) {
var navc=new Image (52,32);
var navcover=new Image(52,32);
navc.src="Images/navcenter.gif";
navcover.src="Images/navcenterp.gif";
}
else {
navc="";navcover=""; navb="";navbover=""; document.navcenter1="";document.navcenter2=""; document.navcenter3="";document.navcenter4="";
}</script>

//-->
</head>
<body>

<a href="index.htm" onMouseOver="document.navcenter1.src=navcover.src" onMouseOut="document.navcenter1.src=navc.src" ><img name="navcenter1" src="Images/navcenter.gif" width="52 height="32"></a>

<a href="about.htm" onMouseOver="document.navcenter2.src=navcover.src" onMouseOut="document.navcenter2.src=navc.src"><img name="navcenter2" src="Images/navcenter.gif" width="52" height="32"></a>

and so on...
</body>
</html>

Thanks in advance. This is killing me.