<script type="text/javascript">      
function op(obj){      
if(document.getElementById){      
var el = document.getElementById(obj).style.display = "block";      
var ar = document.getElementById("masterdiv").getElementsByTagName("div");      
for (var i=0; i<ar.length; i++) { if (ar[i].className=="minfa") ar[i].style.display = "none";}      
}      
}      
</script>      
<a href="javascript://" onClick="op(i1); return false;">Оснавная инфа</a> <a href="javascript://" onClick="op(i2); return false;">Дополнительная инфа</a>      
<div id="masterdiv">      
<div id="i1" class="minfa">$BRIEF$</div>      
<div id="i2" style="display:none" class="minfa">$MESSAGE$</div>      
</div>