""philippe.taymans"" ...

>I have download the zip that you suggest but the problem remain the same
> Just copying all these files is clearly not enough.
> There is something strange : the message says that the DLL can't be
> located but it is there, in the running .exe directory and also (I
> tested it) in the Windows system32 directory

You need to replace existing dll's in your application folder by this files.
Also don't forget to rename fbembed.dll from this package to gds32.dll as
your application requires.

> Can somebody tell me what the Firebird (2.1) installer exactly does ?
> When using it, it works fine ...

Its installed MSVC8 runtime. This was discussed and explained many
times in this list.

Regards,
Vlad