I changed your code like this
<head>
<script language="JavaScript">
loadImage1 = new Image();
loadImage1.src = "Images\Buttons2.png";
staticImage1 = new Image();
staticImage1.src = "Images\Buttons1.png";
</script>
<title> DGC </title>
</head>
<body bgcolor="0e1113">
<center> <img src="Images\Header1.png" width="1250" height="250"> </img></center>
<br><br>
<a href="http://www.google.co.uk" onmouseover="image1.src=loadImage1.src;" önmouseout="image1.src=staticImage1.src;">
<img name="image1" src="Images\Buttons1.png" border="0"> </img></a>
</br></br></body>
and this is working fine
just removed
<-- begin part I could not understand why r you using this.
If you want to create Mouseover Menus search on google you will find a lot like
Pure CSS Menus[
^]
Dropdown menu utility - Using Javascript, CSS and DOM[
^]