Bravo mon vieux!
Wasn't it ever thus? I've just had roughly the same problem with some third-party software; every time I tried to load the Nero CD burner my Win2K PC rebooted! So I uninstalled the last application I had installed from Sitecom (bad earlier experiences with them) and, as you say. hey presto!
We all learn from these exchanges but I can't figure why the event viewer would show DNS errors after you fiddled with the guest account. But who cares as long as it works?