[update] .NET Framework 3.5 Service Pack 1
 

The .NET Framework 3.5 Service Pack 1 (SP1) delivers:

Performance increases between 20-45% for WPF-based applications – without having to change any code
WCF improvements that give developers more control over the way they access data and services Streamlined installation experience for client applications
Improvements in the area of data platform, such as the ADO.NET Entity Framework, ADO.NET Data Services and support for SQL Server 2008’s new features

go to the download page: http://msdn.microsoft.com/en-us/netf.../aa569263.aspx

if you have high speed connect then use the bootstrap option or NET Framework 3.5 Service Pack 1 (Full Package) download and save it