Unsuccessful Vista downloads

I use Vista Home 32 bit. An attempted auto download on 23 August was unsuccessful and the message came on telling me not to turn the pc off as it was reverting the previous action. The unsuccessful update was:
Microsoft .NET Framework 3.5 Service Pack 1 and .NET Framework 3.5 Family Update (KB951847) x86

Installation date: ‎23/‎08/‎2009 13:13

Installation status: Failed

Error details: Code 80070BC9

This happens each time I turn the pc on and is very frustrating and timewasting. This still happens even although one recent download of the same item is shown as successful. Another update unsuccessfully installed today is:

Update for Windows Vista (KB955430)

Installation date: ‎18/‎09/‎2009 10:34

Installation status: Failed

Error details: Code 800F0825

Update type: Important

Install this update to enable future updates to install successfully on all editions of Windows Vista. This update may be required before selected future updates can be installed. After you install this item, it cannot be removed. This update is provided to you and licensed under the Windows Vista License Terms.


I don't know whether this is a common downloading problem or perhaps relating just to my pc. I'm non-technical and any help will be very welcome.

Peter

You have to remove NET Framework 3.5 by using NET Framework Cleanup Tool Aaron Stebner's WebLog : .NET Framework Cleanup Tool User's Guide
and next reinstall again NET Framework 3.5 from full package http://download.microsoft.com/download/2/0/e/20e90413-712f-438c-988e-fdaa79a8ac3d/dotnetfx35.exe

and then istall all hotfixes relate to 3.5

EDIT
KB955430 install from Microsoft Download Center
http://support.microsoft.com/?kbid=955430

Thanks Flavius. I'll try that.