Prueba con esto Código PHP:
<html>
<head>
<title>Untitled</title>
</head>
<body>
<script>
var clickeado;
</script>
<style>
img{cursor:pointer;
cursor:hand;
</style>
<img id="1"
style="position:relative;top:0px;"
onmouseover='anterior=document.images[4].src;this.src=this.src.split("-")[0]+"-1.jpg";document.images[4].src=this.src.split("-")[0]+".jpg"'
onmouseout='this.src=this.src.split("-")[0]+"-0.jpg";if(clickeado!=this)document.images[4].src=anterior;'
onclick="clickeado=this;"
src="http://www.limadata.com/zippo/ayudame/imagenes/2123-0.jpg"><br>
<img id="2"
style="position:relative;top:30px;"
onmouseover='anterior=document.images[4].src;this.src=this.src.split("-")[0]+"-1.jpg";document.images[4].src=this.src.split("-")[0]+".jpg"'
onmouseout='this.src=this.src.split("-")[0]+"-0.jpg";if(clickeado!=this)document.images[4].src=anterior;'
onclick="clickeado=this;"
src="http://www.limadata.com/zippo/ayudame/imagenes/3001-0.jpg"><br>
<img id="3"
style="position:relative;top:60px;"
onmouseover='anterior=document.images[4].src;this.src=this.src.split("-")[0]+"-1.jpg";document.images[4].src=this.src.split("-")[0]+".jpg"'
onmouseout='this.src=this.src.split("-")[0]+"-0.jpg";if(clickeado!=this)document.images[4].src=anterior;'
onclick="clickeado=this;"
src="http://www.limadata.com/zippo/ayudame/imagenes/3143-0.jpg"><br>
<img id="4"
style="position:relative;top:90px;"
onmouseover='anterior=document.images[4].src;this.src=this.src.split("-")[0]+"-1.jpg";document.images[4].src=this.src.split("-")[0]+".jpg"'
onmouseout='this.src=this.src.split("-")[0]+"-0.jpg";if(clickeado!=this)document.images[4].src=anterior;'
onclick="clickeado=this;"
src="http://www.limadata.com/zippo/ayudame/imagenes/3144-0.jpg"><br>
<img style="left:140px;top:10px;position:absolute;" id="grande" src="http://www.limadata.com/zippo/ayudame/imagenes/fijo.jpg">
</body>
</html>