Check the source, already includedhttps://github.com/FirebirdSQL/firebird/blob/v5.0.2/builds/install/arch-specific/win32/FirebirdInstall.iss
May be "Sakkie" is asking how to include VCRT installation in his application Inno Setup?Then inspiration can be taken from Firebird Inno Setup as pointed out by "ttomas"
I have no problem connecting to FB5.In fact, client still using FB3 to connect to FB5 server.Just put fbclient.dll and msvcs100.dll in the same folder of your exe file and make sure that your app use this dll. This worked for client with FB3.