function checkString(obj_id)
{
	var inputObj = document.getElementById(obj_id);
	if (inputObj.value == '')
	{
		alert("The " +  inputObj.name + " field is empty. Please fill it in order to proceed.");
		inputObj.focus();
		return false;
	}
	else
		return true;
}

function checkEmail (emailStr) 
{
	var emailPat=/^(.+)@(.+)$/
	var specialChars="\\(\\)<>@,;:\\\\\\\"\\.\\[\\]"
	var validChars="\[^\\s" + specialChars + "\]"
	var quotedUser="(\"[^\"]*\")"
	var ipDomainPat=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/
	var atom=validChars + '+'
	var word="(" + atom + "|" + quotedUser + ")"
	var userPat=new RegExp("^" + word + "(\\." + word + ")*$")
	var domainPat=new RegExp("^" + atom + "(\\." + atom +")*$")
	
	var matchArray=emailStr.match(emailPat)
	if (matchArray==null) {
		alert("Email address seems incorrect (check @ and .'s)")
		return false
	}

	var user=matchArray[1]
	var domain=matchArray[2]

	if (user.match(userPat)==null) {
	    alert("The username doesn't seem to be valid.")
	    return false
	}

	var IPArray=domain.match(ipDomainPat)
	if (IPArray!=null) {
	  for (var i=1;i<=4;i++) {
	    if (IPArray[i]>255) {
	        alert("Destination IP address is invalid!")
			return false
	  	}
	  }
	  return true
	}

	var domainArray=domain.match(domainPat)
	if (domainArray==null) {
		alert("The domain name doesn't seem to be valid.")
	    return false
	}

	var atomPat=new RegExp(atom,"g")
	var domArr=domain.match(atomPat)
	var len=domArr.length
	if (domArr[domArr.length-1].length<2 || 
	    domArr[domArr.length-1].length>3) {
	   alert("The address must end in a three-letter domain, or two letter country.")
	   return false
	}

	if (len<2) {
	   var errStr="This address is missing a hostname!"
	   alert(errStr)
	   return false
	}

	return true;
}

function centerWindow(window, width, height)
{
	var w = screen.availWidth, h = screen.availHeight;
	if (document.all) {
	   /* the following is only available after onLoad */
	   w = document.body.clientWidth;
	   h = document.body.clientHeight;
	}
	else 
		if (document.layers) {
		   w = window.innerWidth;
		   h = window.innerHeight;
		}

	var popW = width, popH = height;
	var leftPos = (w-popW)/2, topPos = (h-popH)/2;

	window.moveTo(leftPos, topPos);
}