Wireless network sharing safe?

that depends on where you are seeing them

If you are seeing them in "my network places" that means you are able to access them, and they are able to access you

If you are seeing them in your "connect to network" that means there are networks by those names.

To avoid invasion in your computer, when you connect to the network, you should identify it as a public network, then your computer will automatically block the "other" computers from being able to see your computer

Yes, other computer users can see what you see on your computer.  Check out this article .

Just because you can 'see' another computer does not mean you access any information on that computer and vice versa.  Just because they can 'see' you does not mean they access your information.  If you have never shared a file or folder then your information is safe. I believe that as long as you're running windows xp or later then the steps given by curiousone are correct, though generally not necessary.