Download the .tar.gz from Cisco Networking Academy; you need an account, but it’s free.
Extract the .tar.gz to the location of your choice.
Run the install script as a normal user; this means you have to install to a location where your user has write privileges.
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Do not give the script your root password** when it prompts you. Why? Because the script writes to /etc/profile at the end, which it shouldn’t do at all, and it does it in a way that completely messes up bash: “su -” no longer worked for me after I let the script modify /etc/profile (it would just hang), and I had to copy a clean /etc/profile from another computer to get it working again.
Optionally, add PT7HOME=/path/to/bin (use the actual path to the bin directory where PacketTracer7 is located) to your .profile in your home directory. You will need to do this if you want to associate .pkt and .pka files with PacketTracer so you can open them just by double-clicking.
Run PacketTracer either directly from the PacketTracer7 executable located in the /bin subdirectory of wherever you installed, or from the packettracer launch script (which just sets PTDIR to the bin directory and then runs PacketTracer7).
The program installs most of the libraries it needs in its bin directory, and uses them, however, there seems to be some problem with the libcrypto.so.1.0.0 that PacketTracer 7.2 installs. On my system, the program segfaulted after the splash screen with a complaint in the terminal about missing the version info for libcrypto.so.1.0.0. I got around that by renamed PacketTracer’s libcrypto.so.1.0.0 to libcrypto.so.1.0.0.bak, which forced the program to use the system version of that library. It started up without any problems after that.