What are the general steps I want to take to get a program installed on Ubuntu when the program has not been made into a package, or I need an updated software version from what would normally be installed and that version is available in a later repository?
I'll give you my specific example. I'm currently using 10.04LTS and I don't want to upgrade. I want to install the expect-lite package, but it's only available for Ubuntu 11.10 (Oneiric Ocelot) http://packages.ubuntu.com/oneiric/expect-lite
The decision tree I think I want to implement is the following (I think I'm currently at step #3):
apt-get install #if available (or by using the GUI package manager)
Enable universe and multiverse if not already and repeat step 1.
Install a package from a later version of Ubuntu. (How? What pitfalls do I need to watch for?)
install a package from an unstable version of Debian. (same questions from above)
Find and Install a package from Ubuntu's PPA (personal package archive), realising that packages are not reviewed for malicious backdoors or trojans, and this risk could be unacceptable to many people)
If one has the ability, create a personal package from source, and install that (and upload it to the PPA archive if possible to make it available to others)
Install directly from source, and make a dummy package to deal with any dependency issues (knowing full well that this could cause issues if a distro upgrade was attempted later) (info: http://eric.lubow.org/2010/system-administration/creating-dummy-packages-on-debian/ )
Install directly from source as a last ditch effort.
Edited to add:
Use the package Alien to convert a .rpm package to a .deb and then install (see this)
(from BlueXrider's answer below) See if you can find the package in a non-standard repository or download a .deb file from a trusted source and use that.