To answer a question on a previous blog post - YES, there is a PowerShell Add-In for Visual Studio - the VSCmdShell. It works with Visual Studio 2005 and Visual Studio 2008 (I tested with 2008 version) and you can also get the code for it from the project home on codeplex.com.

More about it here:

VS Command Shell - Home

Bertan's Blog

Additional Resources: PowerShellLanguage - .NET Reflector Add-In,  PowerShell Debug Visualizer,  Creating a Windows PowerShell CmdLet using the Visual Studio Windows PowerShell Templates, Building and Debugging Powershell cmdlets in the VS IDE, NetBeans Support for PowerShell