The ISO images are available here:
Milestone m27, standard image
Milestone m27, minimal image
Milestone m26, standard image
Milestone m26, minimal image
Milestone m25 update 3, standard image
Milestone m25 update 3, minimal image
The m20 ISO for SPARC is a little experimental, as it hasn't been tested as well as I would like. You will need a
zap refresh before installing any packages.
You can upgrade a 0m16 SPARC install to 0m18 - Release Notes.
You can upgrade a 0m18 SPARC install to 0m20 - Release Notes.
The SPARC version is experimental, although Milestone 20 is vastly improved. Tested on a T5140, both physical and in an LDOM, a SunBlade 1500, and a SunBlade 2000; status is "works for me".
You don't need to download the ISO, you can run Tribblix in the cloud.
Some older images are also available.