function validate_field(field, alert_text)
{
	with(field)
	{
		if(value==null||value=="")
		{
			alert(alert_text);
			return false;
		}
		else 
		{
			return true
		}
	}
}

function validate_form(form)
{
	with(form)
	{
		if(!validate_field(email,"Please enter your email address!"))
		{
			email.focus();
			return false;
		}
		var filter = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
		if (!filter.test(email.value)) 
		{
			alert("Please enter a valid email!");
			return false;
		}
		if(!validate_field(username,"Please enter your desired user name!"))
		{
			username.focus();
			return false;
		}
		if(!validate_field(password,"Please enter your desired password!"))
		{
			password.focus();
			return false;
		}
		return true;
	}
}