ISO disk images are single files that represent the entire contents of a CD, DVD, hard disk or other piece of computer media. "Mounting" an ISO file on a "virtual drive" tells your operating system to act as if the ISO were a physical disk inserted in a drive or directly connected to the computer--you can access the files in the ISO just as if you'd inserted a CD. How to mount an ISO depends on your operating system.
Use Microsoft's free utility to mount ISOs in Windows XP. Download the utility from the link in "Resources" and double click the downloaded EXE to extract it.
Copy the "VCdRom.sys" file to your "C:\Windows\system32\drivers" folder.
Double click "VCdControlTool.exe" and click "Driver Control." If the "Install Driver" button is not greyed out, click it, browse to and select the "VCdRom.sys" file you put in your drivers folder, and click "Open." Click "Start," then "OK." The driver is now active.
Click "Add Drive" until a drive is created with a letter not already used by a drive in your computer. (Most users will only have to click it once.) Select the drive you've created and click "Mount." Browse to and select the ISO file you want to mount, and click "OK."
Use a third-party utility to mount ISO files, as Microsoft's utility does not work on versions later than XP. The following utilities are both free, and available from links in "Resources."
Download and install Virtual CloneDrive. Once it's installed, you can double click on an ISO file to mount it on VCD's virtual drive.
Download and install DaemonTools Lite, the stripped-down free version of the larger DaemonTools image management software. Once it's installed, click the DaemonTools tray icon and select an empty virtual drive. This will bring up a dialogue box where you can browse to and select the ISO you want to use.
Double click on an ISO file to mount it immediately in Mac OS X. If this doesn't work for some reason, you can mount manually through OS X's "Disk Utility." Click "Applications," then "Utilities" then "Disk Utility."
Click "File," then "Open Disk Image."
Browse to and select the ISO you want to mount. It will appear as a drive on the desktop.