I wanted to take a minute and clarify the difference between Microsoft Visual Studio codename "Orcas" CTPs and "Visual Studio 2005 extensions for .NET 3.0 (WCF & WPF), November 2006 CTP".

Visual Studio 2005 extensions for .NET 3.0 (WCF & WPF), November 2006 CTP
This is a product that can be installed on top of Visual Studio 2005.  This product enables Visual Studio 2005 customers to begin developing .NET 3.0 based applications by providing a set of project templates, WPF designer, and WCF services integrated into VS 2005.  This product is available as a stop gap to enable .NET 3.0 development until the Microsoft Visual Studio Orcas product is released to manufacturing.  Though this product is named November 2006 CTP for consistency with other related releases there will not be any future releases of this product.  November 2006 CTP was the last release of this add-on to VS 2005.

It is important to note that this product underwent a name change in November.  This will hopefully clarify which product to use in the future but may have provided some initial confusion for existing users.  This product has always been codenamed Fidalgo but until November it had previously been publicly named Visual Studio codename "Orcas" development Tools .NET Framework 3.0 CTP.  This name was being confused with the product described next and so we changed the name for our final CTP to the name above.

Microsoft Visual Studio codename "Orcas" CTPs
This product is an early look at the next version of the full Visual Studio product  This new and upcoming version of Visual Studio will have support for building .NET 2, 3 & 3.5 applications and have a suite of other new features.  This release will be a standalone release that will not require VS2005.  Microsoft Visual Studio codename "Orcas" CTP will have built in the functionality currently available in VS 2005 + "VS2005 extensions for .NET 3.0 (WCF & WPF), November 2006 CTP".  As of today Microsoft Visual Studio codename "Orcas" CTP does not have all the functionality available in "VS2005 extensions for .NET 3.0 (WCF & WPF), November 2006 CTP" yet.

This product has released a September CTP and will be release periodic ongoing CTPs with varying functionality until it RTMs.  When this product RTMs it will replace VS2005 extensions for .NET 3.0 (WCF & WPF), November 2006 CTP as the preferred method of developing .NET 3.0 applications and so VS2005 extensions for .NET 3.0 (WCF & WPF), November 2006 CTP will be removed from our download servers.

What should you use?
If you are looking to evaluate what features will be in the next version of Visual Studio then you should install Microsoft Visual Studio Codename "Orcas" CTPs.  Here you will be able to see where the next version of VS is going.

If you are looking to get up and running with building .NET 3.0 applications quickly then you should install VS2005 extensions for .NET 3.0 (WCF & WPF), November 2006 CTP on top of VS 2005.

I hope this helps address some of the confusion between these two products.