Service Pack 3 would work too. If you already have SP3, then you do not need SP2.
Run the downloaded executable and click Next.
Select I have read and accept the license terms and click Next.
Optionally select MSDN Express Library for Visual Studio 2008, which contains complete documentation on the ANSI C standard library and the STL for C++. It is a large download, but download speeds are around 2 MB/s on a fast connection. Click Next.
Click Install.
Wait for the download and installation to complete. Expect to reboot once. Also expect the .NET Framework 3.5 installlaiton to take a while. Click Exit when all is done.