Just those few steps will drastically reduce the potential for serious invasion of your privacy. Most cases of data getting into the wrong hands are still from physical access to the machine the data is stored on. And think about what's on the computer before you make that decision. Also, don't write all your passwords down somewhere that a snoop, invited or not, can easily find them. That takes care of the doors.
Windows are another problem.
For all its convenience and ease of use, Windows is one of the least secure operating systems ever created. Fortunately, there's software that can fix this problem, and fairly easily at that. It's called a firewall. Firewalls make your computer virtually invisible to anyone on the network. One of the best is Zone Alarm.