AS Ivct says it's an iso file and it needs to be burnt to cd with imagburn or similar and your boot sequence needs to have the dvd/cd player first in the list.
I've copied my instructions to here:
"Install Imgburn. OPen it. Where it says: Please Select A File click on the icon on the same line to the right and find the Ophcrack ISO and click on it then OK. Insert disk. Select: Write Image File to Disk (select a slow speed first). Leave disk in tray and make sure your computer is set to boot from CD first in the BIOS.
Leave it and don't touch anything ..leave it to do its stuff. At the first screen make sure it's on Auto (first option). Press Enter or leave it if it's on that.
In the bottom section you'll see the RAM progress bar filling up slowly....when it reaches 100% you should see the password in the top section.
Logout and reboot without the disk in. Enter your password"