If you have been using the 'official' IDPA scoring software (either the original version, or the 2005 release that supports ESR), you can import your shooters database into ForScore.  This will only be successful if you have not modified the format of the IDPA database.

 

In the folder in which you've installed ForScore is a program called FSImport.exe.  Run it and follow the wizard's instructions.  You can either try to add these records to your present shooters list, or start a new shooters list based on what you import.