Use /SP- /SILENT /NORESTART /NOICONS
/COMPONENTS="ServerComponent,ClientComponent" as parameters.

where "Components" can be:
servercomponent,devadmincomponent,clientcomponent

Description of the other parameters (Extract from Innosetup-Help):

/SP-
Disables the This will install... Do you wish to continue? prompt at the
beginning of Setup. Of course, this will have no effect if the
DisableStartupPrompt [Setup] section directive was set to yes.


/SILENT, /VERYSILENT
Instructs Setup to be silent or very silent. When Setup is silent the wizard
and the background window are not displayed but the installation progress
window is. When a setup is very silent this installation progress window is
not displayed. Everything else is normal so for example error messages
during installation are displayed and the startup prompt is (if you haven't
disabled it with DisableStartupPrompt or the '/SP-' command line option
explained above)
If a restart is necessary and the '/NORESTART' command isn't used (see
below) and Setup is silent, it will display a Reboot now? message box. If
it's very silent it will reboot without asking.


/NOCANCEL
Prevents the user from cancelling during the installation process, by
disabling the Cancel button and ignoring clicks on the close button. Useful
along with /SILENT.


/NORESTART
When combined with /SILENT or /VERYSILENT, instructs Setup not to reboot
even if it's necessary.


/LOADINF="filename"
Instructs Setup to load the settings from the specified file after having
checked the command line. This file can be prepared using the '/SAVEINF='
command as explained below.
Don't forget to use quotes if the filename contains spaces.


/SAVEINF="filename"
Instructs Setup to save installation settings to the specified file.
Don't forget to use quotes if the filename contains spaces.


/LANG=language
Specifies the language to use. language specifies the internal name of the
language as specified in a [Languages] section entry.
When a valid /LANG parameter is used, the Select Language dialog will be
suppressed.


/DIR="x:\dirname"
Overrides the default directory name displayed on the Select Destination
Directory wizard page. A fully qualified pathname must be specified. If the
[Setup] section directive DisableDirPage was set to yes, this command line
parameter is ignored.


/GROUP="folder name"
Overrides the default folder name displayed on the Select Start Menu Folder
wizard page. If the [Setup] section directive DisableProgramGroupPage was
set to yes, this command line parameter is ignored.

/NOICONS
Instructs Setup to initially check the Don't create any icons check box on
the Select Start Menu Folder wizard page.


/COMPONENTS="comma separated list of component names"
Overrides the default components settings. Using this command line parameter
causes Setup to automatically select a custom type.



to get this list try starting the setup with the following parameter:
/SAVEINF="filename"
See the descriptions above.


Pay attention if you use "/silent"-setup on a win 9x system. The
firebird-server is not running after the setup finished - on WinNT+ the
server is running. Perhaps you should force a system reboot on Win 9x
machines.

regards
Thomas