Have you got an *.iso image file with media/software that you wish to access without having to burn it to a DVD/CD? This entry explains how to do it on Windows XP/Vista.
ISO images are binary files that contains an exact copy of a DVD or a CD. Typically it is burned to a DVD/CD, which is then put in the DVD/CD drive. However, if you like me got a notebook that does neither have a CD/DVD reader nor a burner, you probably find this a bit annoying, especially as it should be possible to live without the now 25-year old CompactDisc (CD) technology (the DVD technology is ~10 years old). The solution is to mount the ISO file as a virtual drive such that it can be accessed as if it was real DVD/CD.
This is how I did it on Windows XP Pro English edition:
1. Install MagicDisc:
The easiest way to mount an ISO is to install the MagicISO Virtual CD/DVD-ROM software (MagicDisc; download the first item unless you have a Windows 64-bit operating system which most people don't). The MagicDisc is freeware (and free from adware). The installation is easy and straightforward and without hard-to-understand technical options, and there is no need to reboot after the installation. The program will install itself in the traybar (lower-right corner) and there you will also see a Windows notification bubble reporting "Found new hardware...". The program is also available from the Start menu.
2. Mount the ISO file:
To mount an ISO file, just right-click on the MagicDisc icon in the system traybar to get its menu and select 'Virtual CD/DVD/ROM' -> 'D: No Media' -> 'Mount ...'. This will open a file dialog 'Mount CD/DVD image'. Locate and select the ISO file (and click 'Open'). That's it - the CD/DVD will now show up with its own drive letter (here D:) under 'My Computer'.
If the default drive letter overrides another drive you already have mounted, say an external HDD, then use 'Virtual CD/DVD/ROM' -> 'D: No Media' -> 'Change Drive Letter...' to set it to say 'Z:'.
3. Unmount the ISO file:
When done, right-click and do 'Virtual CD/DVD/ROM' -> 'D: somename.iso' -> 'Unmount ...'. If you have mounted a file on an external USB harddrive, you might also have to exit MagicDisc (right-click), before you can remove the USB drive.
Final comments: I actually started to Daemon Tools Lite, but since the installation was lengthy and required a restart of the computer, and after reading others (Mount ISO Files in Windows Vista, Sept 2008) warnings that they add (optional) adware, I decided to go with MagicDisc (v2.7 build 105), which seems to work very well.