I haven't found a useful answer to similar questions. I have downloaded Ubuntu 12.01 to my desktop running Windows 7 and it seems to work fine. But I want to make a CD/DVD to be able to boot Linux on another desktop PC. I can see that I get an ISO file as a result of the download, but as soon as I unzip it there is no longer an ISO file. Please help. Finn Nielsen
There is no need to unzip an ISO file. You can burn it directly to CD using Brasero if you're already using Ubuntu, or if you are using Windows, you can use programs like Nero, PowerISO, or WinISO.
While some archive programs will let you treat an ISO file like an archive and extract its contents, fundamentally an ISO file is an image for a disk. Extracting the ISO is a completely separate operation than burning it, which is what you want to do.
The official installation instructions explain how you can burn the ISO on a Windows system, after downloading it.
For more information and other programs that you can use, see this page.