function doAjax(callback, url, contextVars) {	
	try
	  {
	  // Firefox, Opera 8.0+, Safari
	  xmlHttp=new XMLHttpRequest();
	  }
	catch (e)
	  {
	  // Internet Explorer
	  try
	    {
	    xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
	    }
	  catch (e)
	    {
	    try
	      {
	      xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
	      }
	    catch (e)
	      {
	      alert("Your browser does not support AJAX!");
	      return false;
	      }
	    }
	  }
	  xmlHttp.onreadystatechange=function(){
	  	callback(xmlHttp, contextVars);
	  }	    
	  xmlHttp.open("GET",url,true);
	  xmlHttp.send(null);	  	  
}

function disableForm() {
	var formElems = document.forms[0].elements;
	for (var i = 0; i < formElems.length; i++) {
		formElems[i].disabled=true;
	}	
}

function enableForm() {
	var formElems = document.forms[0].elements;
	for (var i = 0; i < formElems.length; i++) {
		formElems[i].disabled=false;
	}		
}

function showText(textBlockId) {			
	var textBlock = document.getElementById(textBlockId);			
	if (textBlock.style.display=="block") {
		textBlock.style.display="none";
	} else {
		textBlock.style.display="block";
	}
}

function rollOverImage(imageId, imageFileName) {
	var image = document.getElementById(imageId);
	image.src = "img/proj/" + imageFileName;
}

function rollOutImage(imageId,imageFileName) {
	var image = document.getElementById(imageId);
	image.src = "img/proj/" + imageFileName;
}

function checkAll(masterCheckbox, checkboxesName) {
	var checkAll = document.getElementById(masterCheckbox);
	var checkboxes = document.getElementsByName(checkboxesName);
	for (var i = 0; i < checkboxes.length; i++) {
		checkboxes[i].checked = checkAll.checked;
	}				
}