Getting Timeline
Timeline runs on multiple platforms. If you can run Python and wxPython you should be able to run Timeline.
Binary packages are available for Windows systems. If you are on a different system you have to install from source.
If you have problems installing Timeline, send an email to the user mailing list and ask for help: thetimelineproj-user@lists.sourceforge.net.
Versions
The latest version of Timeline is 0.19.0, released on 30 December 2012. To learn what has changed in this version, have a look at the release notes. Older versions are available for download here.
If you would like to get notified whenever there is a new release of Timeline you can subscribe to the news feed on the home page. Or you can subscribe on Timeline's freshmeat page.
Installing on Windows
The binary package for Windows installs an executable version of Timeline built with py2exe. It is a self contained executable that doesn't need any other dependencies to be installed.
Download SetupTimeline0190Py2Exe.exe and execute it.
Installing on other systems (installing from source)
Download timeline-0.19.0.zip and follow the instructions in the INSTALL file.