Hi,
The NI-488.2 for Solaris, v2.2 requires Solaris 2.5.1 or above, and the NI-488.2 for Solaris, v2.3 requires Solaris 2.6 and above. You will see these messages when you start up the installers. You are right that this information should be more clearly available at the website, at the download pages and perhaps in KnowledgeBase, too.