How can I install or update this software that isn't in the repository
 

I've wasted hours trying to install the latest version of Zoneminder, with no luck.

I'm using Debian 7 Wheezy. In the repository, there is version 1.25 . It installed with no problems. However there is a 1.26 which I want to use, which I can download in tar.gz , but everything I have tried has not worked.

I've tried using the make commands, and tried checkinstall, but neither worked (maybe I'm doing it wrong). The zoneminder forums are dead, the info in the zoneminder wiki did not work (using the make command).

Can anyone help me get this installed?

There are a couple of ways you can do this
1. Download the Sid version from this page and install it. I haven't tried it so I don't know if there will be dependency issues or not.
2. Add Sid to your sources list and install the Sid package using Synaptic after updating apt. Make sure after installing it you comment out Sid from your sources.list.
3. Make a deb package from the source (but the download page at Zoneminder tells you about the above package) using the instructions on this page.

Perfect, thanks so much. Searching with the keyword "sid" got me in just the right direction. I added this to my sources.list file

deb http://ftp.de.debian.org/debian sid main

and then was able to upgrade automatically via apt-get. I had tried searching for a "unstable" version before, but came up empty handed without knowing the proper "sid" lingo.