Hi

> I'm about to setup a new DB server where I plan to use FB 2.1. When I
> have client applications, that need to connect to different servers
> (1.5 and 2.1):

> - which fbclient.dll should I use ?

Either will work if you are using TCP/IP to connect to the server. If
you are using the local transport, Firebird 2.0 introduced a new
protocol for local connections which requires client dll to be exactly
the same version as the server. More details can be found in the
release notes: http://www.firebirdsql.org/rlsnotes/Firebird-2.0.4-ReleaseNotes.pdf

> - if I use fbembedded.dll as client library, which one should I use here?

The on disk structure (ODS) has changed between 1.5 and 2.1. If you
are wanting to read databases created using the ODS used by Firebird
2.1, you need to make use of the Firebird 2.1 embedded library.

Regards
Gareth Marshall