In Inno use the [Run] Section to install any third party installations. Something like this:
Code:
[Run]
Filename: {tmp}\VistaDBServerService.exe; Parameters:/install /silent; Flags: skipifdoesntexist; WorkingDir: {tmp}
Filename: C:\Windows\System32\net.exe; Parameters:start VistaDB Server; Flags: skipifdoesntexist
Filename: {tmp}\ServerServiceManager.exe; Flags: skipifdoesntexist; WorkingDir: {tmp}
Of course you will need to include these files in your [Files] Section to be included in the original installation. Or you can include them seperately (files not in the [Files] section) and have Inno just run them from the original location or copy them to another location then run them.