It sounds as though you need to configure a proxy server. The (I guess Windows) PCs on the network are probably set up for automatic proxy configuration. That means they will get details of the proxy server they need to use from the DHCP server, but for the tablet you'll have to configure it separately. If you can figure out the url for the WPAD file then you can enter into the tablet's network configuration.
See http://en.wikipedia.org/wiki/Web_Pro...overy_Protocol