Older versions of Garritan libraries were based on the Kontakt 2 Player. If you own an older version of Garritan Personal Orchestra, Garritan Jazz and Big Band, or Garritan Concert and Marching Band, you can purchase a newer version of these libraries at http://www.finalemusic.com/Store/GarritanProducts.aspx?g=1. These products are based on the Garritan ARIA Player and are compatible with newer computers.
Note: Only Garritan Personal Orchestra 4 serial numbers qualify for an upgrade to Garritan Personal Orchestra 5.
If you own the Garritan Stradivari or Gofriller library, or if you want to use your older GPO, JABB, or COMB library on a newer computer, you may be able to use these in a newer version of the Kontakt Player. Contact Native Instruments at http://www.native-instruments.com/en/support/ or by calling (323) 467-2693 in the U.S. to discuss upgrading to a newer Kontakt version.