The new Service Pack 2 for Windows Vista contains a serious bug that will cause your default gateway to vanish at every reboot so your Internet connection won't work if you don't set it manually (or by NetSetMan) after each startup. Hopefully Microsoft will fix this soon with an update. Until then you can do this yourself.
How to solve the problem with the disappearing gateway in Vista SP2:
1. Open the registry with regedit.exe
2. Go to the path: HKLM/System/CurrentControlSet/Services/Tcpip/Parameters/Interfaces/
3. Here you'll need to select the CLSID of your networkadapter where you change the settings. You'll probably recognize it by looking at the value IPAddress that will have the IP of this adapter.
4. Open the value "DefaultGateway" by doubleclicking it. You will see a list of all the gateways that disappeared! Very likely, the first line will be empty. If you now manually remove this first empty line, click OK and reboot your system everything should be working fine again.
