http://www.timeslips.com/
don't mention what underlying database is used. .db may indicate that it's a dbase/foxpro/clipper database (although .db is a common custom extension as well.)
IF they're dbase/foxpro/clipper, then you should be able to use ODBC to connect from Access, & import the tables.
If it's a custom flat file format, you should still be able to connect to it for import; either as a fixed-width format or a character separated format. You'll just need to open the .db file in a hex editor (or even with notepad) to determine the format. Once you've nailed down the format, then you could define an import approach