Shouldn't it be the other way round?
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<head>
</head>
<html>
<body>
<%
Dim str As String = HttpContext.Current.Request.Url.Host
If (String.Compare(HttpContext.Current.Request.Url.Host, "SomeOldWebsiteURL.com", True) = 0) Then
Response.Redirect("index.asp")
End If
%>
</body>
</html>