In Visual Basic 5.0 and 6.0, you could make use of the "InternetCheckConnection" Win32 API located within the WININET.DLL library to detect if the user was connected to the internet. The same API could be used to FORCE an internet connection (meaning if they aren't connected, tell their OS to connect).
Is there a way to do this within .NET? I'm using VB.NET, but sample code in C++.NET, C#.NET, J#.NET, etc is ok to. As long as it's CLR code I can understand it.