>  Why do you think you can't use just v2.5 client ?

>isn't  supported from Zeoslib for Delphi 5 :(

Sounds crazy, sorry. Can you provide a reason for it ? Just curious...

>  Choose any folder you like, put firebird.msg there and set environment variable
>FIREBIRD_MSG pointing to this folder. You should set it before you'll load fbclient.dll.

> In this case, I have conflict with version 2.5 (in this case nt works fine the 2.5 version) because environment
> variable is in system scope. Is there a way to set an environment variable in scope only for application that set it?

Sure. You can
a) run your application using bat\cmd file with two lines
SET FIREBIRD_MSG=<path_to_firebird.msg>
<your_app.exe>

or you can
b) call WinApi function SetEnvironmentVariable before attempt to load fbclient.dll