If you’ve downloaded the beta releases of Windows Vista or Office 2007, you’ve had to deal with the ISO file format, which consists of an image of a CD or DVD. You can use most CD/DVD writing programs to copy the ISO file to a physical disk. In Nero 6, for instance, you use the Burn Image command on the Recorder menu.
In addition, there are software utilities that allow you to read an ISO file or mount it in Windows without burning a physical disk. This MSDN page has some useful links:
Copying the contents of ISO files
The contents of image files may be accessed directly using third-party tools. Using this method you can extract the files from an image file to a temporary folder on your hard drive, then run setup. The following tools offer such image file support:
The products listed above have been known to work. Other products that can manipulate ISO files may work, but have not been tested.
Mounting ISO files virtually
The following tool for Windows XP allows image files to be mounted virtually as CD-ROM/DVD-ROM devices. This tool is provided here for your convenience, and is unsupported by Microsoft Product Support Services.
Nero 6 Ultra Edition (and presumably Nero 7 as well) has an ISO mounting tool called Nero ImageDrive. It’s incompatible with Windows Vista, however, as is the free Microsoft tool linked here.