To read/write dbase files you can use the Microsoft JET OLEDB provider, with a connection string that looks like this one:
Provider=Microsoft.Jet.OLEDB.4.0;Data Source=c:\directory;Extended Properties=dBASE IV;User ID=Admin;Password=
Note that Data Source is the folder where your dbase file is. Finally in your query the table name should be the file name without the .dbf extension, like this:
INSERT INTO netpokl (Castka,Akce) values(@castka,@akce)
Should you need this to work on a 64bit application you can use the Microsoft ACE OLEDB provider (Microsoft Access Database Engine 2010 Redistributable)
Provider=Microsoft.ACE.OLEDB.12.0;Extended Properties=dBASE IV;Data Source=c:\directory;