The 32-bit version of Ubuntu is a complete desktop Linux operating system, freely available with both community and professional support. Ubuntu 14.04 LTS is the current long-term support version with the Unity desktop. Older releases of Ubuntu, prior to 12, use the GNOME desktop and is easier to use for Windows XP/Windows 7 users.
The latest version of Ubuntu can be downloaded here: http://www.ubuntu.com/download.
Older releases can be downloaded here: http://old-releases.ubuntu.com/releases/
Once you have installed Linux, install the TI SDK.