provided information such as what you are trying to install that gives the error and exactly what the error states.

Without knowing specifics all I can do is point you to where you can download the most current version of the Microsoft Installer:

Instmsia.exe for Windows 98 or Windows Millennium Edition:
http://download.microsoft.com/download/WindowsInstaller/Install/2.0/W9XMe/EN-US/InstMsiA.exe
-or-
Instmsiw.exe for Windows NT, Windows 2000 or Windows XP:
http://download.microsoft.com/download/WindowsInstaller/Install/2.0/NT45/EN-US/InstMsiW.exe