If you're running Windows, and you have a CD-burner, then burn the image to a CD (Nero can do this, but I think EasyCD is easier).
If, however, you're running Linux and you're quite happy with keeping this large file on your HD, then mount it:
mount -o loop /isolocation /mountpoint
where
/isolocation is where the .ISO file is (full directory and full filename, press tab for autocompletion) and
/mountpoint is where you want to access the files.
For example, if you've just received an ISO file containing a new distro, you might want:
mount -o loop /root/downloaded/distro.iso /mnt/new-distro
this would mount the distro.iso file into the directory /mnt/new-distro
Obviously, if you're running Linux and you want to burn it to a CD, you can (just not sure how
)
Hope this helps.
software in .ISO file
