New Information on .NET 3.5 Details
A couple of great posts from Aaron Ruckman detailing the .NET Framework 3.5 installation.
Some good overview details about the .NET 3.0 SP1 and .NET 3.5 installers:
How to create a .NET Framework 3.0 SP1 redistributable package since the Microsoft download center presently only has this as a Web download bootstrap:
How you can detect if .NET Framework versions 3.0 RTM, 2.0 SP1, 3.0 SP1 and 3.5 are installed: