Sibelius 7 and later include pre-made sound sets for Garritan Personal Orchestra 4, Jazz and Big Band 3, and Concert and Marching Band 2. These sound sets are also available for Sibelius 6 from Avid's support website at http://www.sibelius.com/helpcenter/resources/soundsets.html.
At this time, Avid has not yet produced a Sibelius sound set for other Garritan libraries. Please consult your Sibelius documentation or contact Avid Support for steps on creating a manual sound set in Sibelius for these libraries.