i never tried reg ex
The only thing which is remain is character counting how much letter submitted in input box.

alert box must show counted characters + valid or invalid email + message


Code: 
<html>
<head>
<script type="text/javascript">
function CheckMyEmail()
{
var x=document.forms["myForm"]["email"].value;
var value=("BC102034568");
var at=x.indexOf("@");
var dot=x.lastIndexOf("vu.edu.pk");
if (at<1 || dot<at+1 || dot+2>=x.length)
{
alert( x + " is Not your valid VU e-mail address");
return false;
}
else
{
    if(x=="BC102034568@vu.edu.pk")
        {
        alert( x + " is your valid VU e-mail address");
        return false;
        }
else
{
alert( x + " is not an valid email address");
return false;
}
}
}
</script>
</head>

<body>
<form name="myForm" action="example.html" onsubmit="return CheckMyEmail();" method="post">
Email: <input type="text" name="email">
<input type="submit" value="Submit">
</form>
</body>

</html>
you again forgot to make return function well i done it.

if someone submit more then 40 characters email the alert box show email it too much large of some one enter minimum characters like 2 or 3 character alertbox must show email characters are less.