format of *.btl files

Hi,
Does anybody know how to build personal *.btl file? I need
a special version for an old dBase database (having an old
Polish "code page" characters - not 852) and I dont want
to convert the files (backward compatibility).
The other possible solution is to "patch" existing, not used table.
Any ideas are welcome.
Thanks in advance.

Mariusz Grecki
gre...@dmcs.p.lodz.pl