Floppy authorizations will not work on OS X. See the iLok Authorization Info quick link in the Support section:
www.digidesign.com/support
For Digi-distributed plug-ins, you would need to download the Pro Tools 6.4.1 for MIX compatible plug-ins from here:
Pro Tools|24 MIX Downloads
Pro Tools will not run on Classic when booted in OS X, so there is no reason to go down that path. If you are using OS X, you will need the iLok authorized versions of the plug-ins.
Some downloads may be compressed as Stuffit (.sit or .sea) files, which would try to launch Classic to open unless you install the free Stuffit Expander for OS X:
http://www.stuffit.com/mac/expander/download.html