Хелпми, пример
melky только с src.
<img id="id" src="http://javascript.ru/forum/images/reputation/reputation_plus.gif"
onclick="ChangeURLPicture()">
<script>
function ChangeURLPicture()
{
abz = document.getElementById("id");
if ( abz.src == "http://javascript.ru/forum/images/reputation/reputation_minus.gif")
{abz.src = "http://javascript.ru/forum/images/reputation/reputation_plus.gif";}
else { abz.src ="http://javascript.ru/forum/images/reputation/reputation_minus.gif";}
}
</script>