Short answer is to get DDFs (FILE.DDF, FIELD.DDF, and INDEX.DDF) that describe the field structure then use ODBC to export the data and then import the data to SQL Server.
You might look at the Pervasive Data Integrator product line. It's designed to move data from one source to a different destination.
You could also export the data to CSV and then use SQL Server to import it.

You will need a PSQL engine of at least the version the data files were created with. In your case, you'll need PSQL at least version 2000.