How do I set up my system to access the Internet through a USB air card and disable it through the LAN. I'll need to access the LAN for files and folders only.
If using a pc, you could use windows firewall to only allow traffic to the lan over specific ports (i.e. the ones that you use to access files/folders). Then block all other traffic to the lan subnet.
you could use 'netstat' in the command prompt while connected to the lan resources to determine what ports are being used.
also, check out Microsoft Network Port Requirements