> Of course I use FB 2.1 official installer.
>
> Firebird-2.1.0.17798_0_Win32.exe
> I had no problems on any of the PC-s that I installed FB 2.1 to.

Check following :

a) you have no msvc8 runtime libraries in system32

b) you have no msvc8 runtime libraries without manifect in your app folder

c) you have no msvc8 runtime libraries without manifect in %PATH%

> Is this
>
> http://www.microsoft.com/downloads/details.aspx?familyid=200B2FD9-AE1A-4A14-984D-389C36F85647&displaylang=en
>
> Microsoft Visual C++ 2005 SP1 Redistributable Package (x86)
>
> the package I am supposed to install ?

No. We didn't used SP1

Regards,
Vlad