12.04 - Can I use 8.04 Hardy packages or repositories on Precise?

I'm using Precise Pangolin, and I sometimes notice packages I'd like to install exist on http://us.archive.ubuntu.com/ubuntu/ hardy main but not on http://us.archive.ubuntu.com/ubuntu/ precise main. I have two related questions:

1. Is it safe to install these packages manually (e.g. by downloading from http://packages.ubuntu.com/hardy?)



2. If so, can I also add the hardy sources to my /etc/apt/sources.list, like so?

   
   

   deb http://us.archive.ubuntu.com/ubuntu/ precise main restricted universe multiverse
   deb-src http://us.archive.ubuntu.com/ubuntu/ precise main restricted universe multiverse
   deb http://us.archive.ubuntu.com/ubuntu/ hardy main
   deb-src http://us.archive.ubuntu.com/ubuntu/ hardy main
   

This is not recommended, probably won't work, and can break your 12.04 system!

1. You can try installing individual Hardy application debs, but there's a good chance they won't work because of dependency (library) problems; if you try to install those Hardy libraries, you will probably break your Precise system.




2. Adding the Hardy repositories to Precise is a very bad idea and will almost immediately break your system.

Once broken, it can be very difficult to fix your system -- updating/upgrades may not work, and Precise applications may not either.

How can I use those "Hardy" applications then?

1. You can try building them from source.


2. But it may be easier to create a Hardy chroot instead -- this allows you to create a Hardy installation within your Precise system, which can use the Hardy repositories, install all Hardy applications, etc. and still run without causing any problems to the main Precise. Please see this Ubuntu guide for more details.