I have an old computer that I only use for storage. I want to have this computer on my network but I don't want it to see or be seen by the internet.
I only want my other computers to see and be seen by the Internet..
How can I do this
A proxy is the way to go. If you have a router or a switch you can manually configure it, but probably that ain't all that necesary, perhaps if only 1 computer is the one connected to the router then check your firewall or proxy config.
just set the IP manually without any gateway and dns. only ip and subnet to match your intranet.
to be totally safe, disable upnp in your router. but that's not really necessary anyway.
OK.. I have got something to go on and learn my way into ..
Good luck with setting this up. It can be difficult depending on how your computer behaves. Sometimes they like to reset to a configuration that you have not used for years and thought you had removed completely. Sometimes they work wonderfully.
Actually, if its an old computer, and you've installed linux on it, it comes with a free firewall called IP tables, which you can use to block everything.
Of course, fi you want to block everything, you might as well just disconnect the network altogether.
If you want to use it as a storage device (pseudo), you could just put a share on it, and have all the other computers in your home access it, although old hardware is generally slow to store and serve files.
There are free firewall / proxy softwares in windows, though none comes to mind right now, except zone alarm, which takes time and patience to use, and pops up everytime you try or the machine tries to access the internet.