The above steps didn't worked for me. Anyways I happened to work it out with the help of debian user list and it worked.
Here are the steps.
1) Assume you have the iso file in /home/iso-files/ folder. I had the debian-7.1.0-amd64-DVD-1.iso in /home/iso-files folder
2) Make a new folder in /media
you will have to run the above command as root
3) Run the following command as root
mount /home/*yourUsername*/iso-files/debian-7.1.0-amd64-DVD-1.iso /media/dvd1-mountpoint -o loop
4) Add an entry to /etc/fstab as follows
/home/*yourUsername*/iso-files/debian-7.1.0-amd64-DVD-1.iso /media/dvd1-mountpoint iso9660 loop,ro,user,noauto 0 0
5) Make an entry in your /etc/apt/sources.list as follows
deb file:/media/dvd1-mountpoint/ wheezy main contrib
6) Comment out everything else in /etc/apt/sources.list by adding a # at the start of every entry. only the above line should be uncommented.
7) Run the following command as root
8) Install any package name and now it should work.
apt-get install somePackage
9) You can check if your entry in fstab is correct or not by unmounting the dvd and then directly mounting the mountpoint
10) If you plan to automount the dvd at start up you should remove user,noauto from entry in /etc/fstab
The above steps are working just perfectly for me. It should work for you also!
I know I am pretty late to answer you, but anyways!