Puoi provare così:
<img src = "1.gif">
<img src = "2.gif">
<img src = "3.gif">
Crei la pagina html
[HTML]<html>
<head>
</head>
<body>
<a href ="#"><img width = "50" height = "50" src = "1.gif" onClick ="document.getElementById('grande').innerHTML = '<img src = 1.gif>';"</a>>
<a href ="#"> <img width = "50" height = "50" src = "2.gif"onClick ="document.getElementById('grande').innerHTML = '<img src = 2.gif>';"></a>
<a href ="#"> <img width = "50" height = "50" src = "3.gif" onClick ="document.getElementById('grande').innerHTML = '<img src = 3.gif>';"></a>
<br>
<div id = "grande"></div>
</body>
</html>
[/HTML]