Project-level FlexTables are available only for the project in which you create them. The Shared FlexTables are available for all projects for the user that created them and are stored in the user's profile. If you create shared FlexTables, they will be in each project that you create or edit.
There is not a way to import FlexTables. If you want all users to use the same FlexTables, you can copy the FlexTables.xml file to a network folder, or send it to each user. If it is in a network folder, each user would need to copy it to their user profile folder (C:\Users\<username>\AppData\Local\Bentley\PondPack\8 on a Windows 7 computer). However, if any one person updates the .xml file, it will need to be redistributed to all users.