Problème silverlight installation

Bonjour voila mon problème je veux installer le plug-in de silverlight 2 pour visual studio 2008 :
http://www.microsoft.com/downloads/details.aspx?FamilyID=c22d6a7b-546f-4407-8ef6-d60c8ee221ed&DisplayLang=fr

J'arrive à télécharger le fichier et je lance l'installation.
L'installation télécharge les données et plante lorsque qu'il commence à installer avec ce message :

Exe (c:\c1d0aaa4ca32cdac03bc\PurgeSLTCache.exe) succeeded.

[7/6/2009, 20:46:50] Action complete

[7/6/2009, 20:46:50] Exists: evaluating...

[7/6/2009, 20:46:50] (IronSpigot::Path::Evaluate) Path: C:\WINDOWS exists.

[7/6/2009, 20:46:50] Exists evaluated to true

[7/6/2009, 20:46:50] (IronSpigot::ExeInstallerBase::ExeInstallerBase) Created new ExePerformer for Exe item
[7/6/2009, 20:46:50] (IronSpigot::CompositePerformerBaseT<class IronSpigot::MsiInstaller,struct IronSpigot::MspInstaller,struct IronSpigot::MultipleMspInstaller,class IronSpigot::ExeSelectingPerformer<class IronSpigot::ExeInstaller,class IronSpigot::CartmanExeInstaller> >::PerformAction) Created new ExePerformer for Exe item

[7/6/2009, 20:46:50] Action: Performing Action on Exe at C:\DOCUME~1\hugo\LOCALS~1\Temp\Silverlight Tools RTW\Silverlight.2.0_Developer.exe...

[7/6/2009, 20:46:50] (IronSpigot::ExeInstallerBase::Launch) Launching CreateProcess with command line = Silverlight.2.0_Developer.exe /q /ignorewarnings
[7/6/2009, 20:47:27] (IronSpigot::ExeInstallerBase::PerformAction) C:\DOCUME~1\hugo\LOCALS~1\Temp\Silverlight Tools RTW\Silverlight.2.0_Developer.exe - Exe installer does not provide a log file name
[7/6/2009, 20:47:27] (IronSpigot::ExeInstallerBase::PerformAction) Exe (C:\DOCUME~1\hugo\LOCALS~1\Temp\Silverlight Tools RTW\Silverlight.2.0_Developer.exe) failed with 0x80070643 - Erreur irrécupérable lors de l'installation. .
[7/6/2009, 20:47:27] (IronSpigot::ExeInstallerBase::PerformAction) PerformOperation on exe returned exit code 1603 (translates to HRESULT = 0x80070643)

[7/6/2009, 20:47:27] Action complete

[7/6/2009, 20:47:27] Action: Performing actions on all Items...

[7/6/2009, 20:47:27] (IronSpigot::ExeInstallerBase::ExeInstallerBase) Created new ExePerformer for Exe item
[7/6/2009, 20:47:27] (IronSpigot::CompositePerformerBaseT<class IronSpigot::MsiUnInstaller,class IronSpigot::MspUninstallerT<class IronSpigot::CMsiInstallContext>,class IronSpigot::MspUninstallerT<class IronSpigot::CMsiInstallContext>,class IronSpigot::ExeSelectingPerformer<class IronSpigot::ExeUnInstaller,class IronSpigot::CartmanExeUnInstaller> >::PerformAction) Created new ExePerformer for Exe item

[7/6/2009, 20:47:27] Action: Performing Action on Exe at c:\c1d0aaa4ca32cdac03bc\PurgeSLTCache.exe...

[7/6/2009, 20:47:27] (IronSpigot::ExeInstallerBase::Launch) Launching CreateProcess with command line = PurgeSLTCache.exe /q
[7/6/2009, 20:47:27] (IronSpigot::ExeInstallerBase::PerformAction) c:\c1d0aaa4ca32cdac03bc\PurgeSLTCache.exe - Exe installer does not provide a log file name
[7/6/2009, 20:47:27] (IronSpigot::ExeInstallerBase::PerformAction) Exe (c:\c1d0aaa4ca32cdac03bc\PurgeSLTCache.exe) succeeded.

[7/6/2009, 20:47:27] Action complete

[7/6/2009, 20:47:27] Action complete

[7/6/2009, 20:47:27] (IronSpigot::LogUtils::LogFinalResult) Final Result: Installation failed with error code: (0x80070643), Erreur irrécupérable lors de l'installation.

Ceci est le message du fichier journal.
J'ai bien visual studio 2008.
D'où vient le problème? d'avance merci pour vos réponses.