function hideRows() {
var allRows = document.getElementsByTagName("tr");
for (i=0; i < allRows.length; i++) {
if(allRows[i].id != "option") {
allRows[i].style.visibility='hidden';
}
}
}
function changeRow() {
var intCount = document.getElementById("selTest").options.length; //gets count of items in select menu
var intValue = document.getElementById("selTest").selectedIndex; //gets number (0 index) of selected item
for (i=0;i<intCount;i++){
var strValue = document.getElementById("selTest")[i].value; //gets value of selected item
if (i == intValue) {
document.getElementById(strValue).style.visibility='visible';
}
else {
document.getElementById(strValue).style.visibility='hidden';
}
}
}
// Event Handler
function addEvent(obj, evType, fn) {
if (obj.addEventListener){
obj.addEventListener(evType, fn, false);
return true;
}
else if (obj.attachEvent) {
var r = obj.attachEvent("on"+evType, fn);
return r;
}
else { return false; }
}
addEvent(window, 'load', hideRows);


P.S. Your code snippets are not showing everything. I had to go to demo page to see all the code.