I had the same proble, a WAN with 4 laptops, 1 Dell XPS M1730 with Windows 7 -64b as server, and 2 laptops with XP3 and 11 with Vista.
Setting up the file SPEED2.EXE with
2- administrator right (right-click on the file, choose "properties", then "Compatibility" tab, then select Run This Program as XP3, and also in Privlege Level, say "Run as administrator")
IT DOES THE TRICK !!!
(be sure also that, when you start, your firewall/antivirus does not block teh communication: ALT+TAB when trying to make a LAN for checking if your firewall does not ask you the authorization for proceeding...)