Litet ex.
<script type="text/javascript">
function checklists(){
var listvalues=new Object();
for(var n=0;n<arguments.length;n++){
var value=arguments[n][arguments[n].selectedIndex].value;
if(value!=0 && listvalues[value]){ return false; }
listvalues[value]=true;
}
return true;
}
</script>
<form>
<select name="lista"><option value="0">0</option><option value="1">1</option><option value="2">2</option></select>
<select name="listb"><option value="0">0</option><option value="1">1</option><option value="2">2</option></select>
<select name="listc"><option value="0">0</option><option value="1">1</option><option value="2">2</option></select>
<input type="button" onClick="if(!checklists(this.form.lista,this.form.listb,this.form.listc)){alert('No no..'); }">
</form>