I decided to write this post after I found myself a little bit lost trying to find customer's answers in the official MSDN documentation about deploying the .NET Framework 3.5 SP1. Luckily at the end I found Aaron Stebner's Blog. Aaron previously worked for the setup team for Visual Studio and the .NET Framework and on his blog I could find really a lot of useful information (a lot of great posts!) for solving all customer ‘concerns. Thanks Aaron!

I will then try to summarize what I find out:

• You can download the .NET 3.5 SP1 Full Package File at http://download.microsoft.com/download/2/0/e/20e90413-712f-438c-988e-fdaa79a8ac3d/dotnetfx35.exe (English).

• The .NET Framework 3.5 SP1 is a slip-stream replacement for the .NET Framework 3.5. What does it mean? That it will install correctly on systems that do not yet have the .NET Framework 3.5. Instead, if you run it on a system that does already have the .NET Framework 3.5, it will automatically upgrade 3.5 to 3.5 SP1 for you.

• The .NET Framework 3.5 SP1 contains all of the prerequisites and hot fixes needed to install the .NET Framework 3.5 SP1 on all operating systems. The .NET Framework 2.0 and 3.0 are part of the OS on Windows Vista, and the .NET Framework 3.5 SP1 contains Windows Vista update packages to apply the .NET Framework 2.0 SP2 and 3.0 SP2 on that OS. You do not need to install anything separately.

• Pay attention if you run .NET Framework 3.5 SP1 on a non-English OS!
  If you run the .NET Framework 3.5 SP1 on a non-English OS, it will attempt to install the .NET Framework 3.5 SP1 language pack in the language that matches the OS language by default. As the language pack is not a part of the full package, the .NET Framework 3.5 SP1 installer will attempt to download it and install it for the user behind the scenes on non-English OS's. If you want to get more information on this specific scenario you can have a look at case 2 described in the following post of Aaron Stebner: http://blogs.msdn.com/astebner/archive/2008/07/17/8745415.aspx (the blog post is about .NET Framework 3.5, but the same behavior exists in the .NET Framework 3.5 SP1).

• The .NET Framework 3.5 SP1 language pack is a slip-stream replacement for the .NET Framework 3.5 language pack. It will install correctly on systems that do not yet have the .NET Framework 3.5 language pack. If you run it on a system that does already have the .NET Framework 3.5 language pack, it will automatically upgrade the 3.5 language pack to the 3.5 SP1 language pack behind the scenes for you.