function validate()
{ 
	var theform=document.loginform;

	var username=theform.username;
	if (username.value=='')
	{
		alert("用户名长度不可少于6个字符");
		theform.imgusername.style.visibility="visible";
		username.focus();
		username.select();
		event.returnValue=false;
		return;
	}

	var password=theform.password;
	if (password.value=='' || password.value.length<6)
	{
		alert("密码长度不可少于6个字符");
		theform.imgpassword.style.visibility="visible";
		password.focus();
		password.select();        
		event.returnValue=false;
		return;
	}
}
function hiddenimg(nameofimg)
{
	nameofimg.style.visibility="hidden";
}