We recently had someone ask if the thesaurus functionality in SharePoint 2003 is still available in MOSS 2007.
Bill English has a good article describing the thesaurus in SharePoint Portal Server 2003. After a little looking around, it appears that the same functionality is still available in MOSS 2007.
The file naming convention and format remain the same, so moving the file from one system to another should be pretty straightforward. I’m assuming that the file is migrated during an upgrade, but will test that out and post if there are any problems experienced with that process.