If you have tried to install SP1 for Visual Studio 2008 and have experienced failure then follow the steps as mentioned below:

These steps applies to if you have Visual Studio 2008 alone, or on the top of some Beta components of SQL Server and Visual Studio 2008.

Tricks before you begin installation:
1- Disable Automatic updates.
2- Disable any of the Anti-virus, spyware etc.
3- Set Windows Firewall to Off.
4- Keep the VS 2008 Installation media ready.

Step -1: Visual Studio 2008 Service Pack Preparation Tool

Step -2: Microsoft Visual Studio 2008 Service Pack 1

In this step-2, you may experience that at the end of installation wizard “SQL Publishing Wizard 1.3” is running forever, if you face the same then cancel the setup, and it will show you the finish dialog. Now you can successfully perform Step-3.

Step -3: Microsoft Silverlight Tools Beta 2 for Visual Studio 2008

Once these steps are performed then you can go to Visual Studio –> Help menu –> About Visual Studio, and you will see that SP1 is installed along with SilverLight as show in the figure below. Also it will install all the updates during the installaion procedure.

The Service Pack1 Beta is available for the .NET Framework 3.5 and Visual Studio 2008. The SP1 comes with new features.

Lets have look here for features and download:

Microsoft .NET Framework 3.5
Service pack 1 Beta

Microsoft Visual Studio 2008 Service Pack 1 Beta