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

function validate_email(field,alerttxt)
{
with (field)
{
apos=value.indexOf("@")
dotpos=value.lastIndexOf(".")
if (apos<1||dotpos-apos<2) 
  {alert(alerttxt);return false}
else {return true}
}
}

function validate_form(thisform)
{
with (thisform)
{
if (validate_required(name,"Please enter your name")==false)
{name.focus();return false}
if (validate_required(email,"Please enter your email address")==false)
{email.focus();return false}
if (validate_required(message,"Please enter your message")==false)
{message.focus();return false}

if (validate_email(email,"I think you've made a mistake with your email address")==false)
{email.focus();return false}

}
}