Entra no SO como Administrador e instala-o, se mesmo assim não der pode ser que a versão do windows Installer seja antiga, o que é estranho tratando-se do XP ?!!
Tens o SP1 p/ o XP instalado ?
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http://mitglied.lycos.de/stereo3d/msiupdate.htm
Microsoft Installer Update
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If setup does not work, you must update Microsoft Installer.
Windows Installer 2.0 for Win9x: InstMsiA.exe (1670 kB)
Windows Installer 2.0 for Windows NT and 2000: InstMsiW.exe (1781 kB)
Windows XP already comes with Windows Installer 2.0, therefore no update is necessary. Many other setups automatically update Microsoft Installer (e.g. Microsoft Office setup) too, so it is very likely that version 2.0 or better is already installed also on Win9x, Windows NT and Windows 2000 systems.
If it setup does not work, install one of these updates.
Espero que ajude.