The simplest way is to loopback mount the file. This will assign one of /dev/loop[0-7] to the file and mount that device - thereby giving you the .iso contents in a directory pretty much identical to if you had burnt the disc. This is done with a normal mount command except that whereas one would normally type:
mount [-t <filesystem>] <dev> <mnt point> [-o <options>]
one now types:
mount [-t <filesystem>] <file> <mnt point> -o loop[,<options>]
i.e. use the file instead of the device and add loop to the list of mount options. You will need to be root to mount/umount the directory - hope this helps.