For security reasons, I have a public and a private LAN which are not connected to each other. Sometimes it would be useful, though, to use a computer between the two LAN´s for exchanging files. This computer should only be connected to one LAN at the time. Is there some kind of hardware (a switch or something) that allows me to switch this "intermediate computer" from the private to the public LAN and back? Does anyone understand what I mean? :)

For all the time and trouble a gig usb stick would be easier. I have a similar setup. I also have a box with two nics. One to the internet and one to the lan. I use hardware profiles to boot one or the other but never both at the same time since that would violate the air gap between the two networks. In your case you can do either of the above or with two nics setup ICS between the two networks. You can disable the nic you don't want to be connected to and/or you would have the ability to "route" between the two for file xfers if you wanted. Understand what I mean? :-) Golly gee wilerkers everyone. Learn to Internet Search

Thanks for replying. I´m not sure I totally understand, but it´s always good to have something to go by. I think I should be able to manage to get more information with the explanations ans terms you gave me. Thanks again!