DNS shouldnt cause a problem if hes trying to rech the site via the IP as a raw IP doesnt need to be reolved into annother IP . . . the system knows this and skips the DNS lookup and just goes for the IP. your welcome to correct me on this but if you for example ping www.google.com, note down what IP it reolved to, remove ALL your DNS setting and typle that IP in (http://xxx.xxx.xxx.xxx/) it will still work as the DNS already did its job by resolving the ping for you, you dont need it again if you remember what the IP was.
as for the vista computer unable to show the shared files ont eh other computers, this is due to Microsoft drastically changing he way vista file sharing works, its has to be enabled from the networka and sharing centre, also the network has to be set as private, and lastley the windows firewall (or other firewall's) on BOTH systems need to be set correctley, this will still not enable it to work and mine still sometimes just disappeares but comes back after you spam F5 a few times. its just abit glitych it seems and sometimes says its not there if you type the pc name yet the browser shows it, or also it wasnt showing AT ALL yet I could select it from the pulldown 'history' and could see the recent changes and download stuff from the other systems despite it now apparently being there...just keep aruing with it, it will just work out of the blue, thats what I found :S