I am trying to setup a holding page stored locally on laptops so if they try to visit the corporate internal intranet site which is set as their homepage it will display the page if they are on the network or the local page if they are external. e.g. "You are not on the network and here are some quick links to webmail etc".

Problem is I have create the local page but getting it to only appear when the site isn't available is well beyond my knowledge! Can anyone help? or ever done similar? maybe a site unavailable page?