MSBUILD 4.0, XmlPeek, XmlPoke, and MSB4036

I installed Visual Studio 2010. I was creating a new MSBUILD file and was delighted to find the new XmlPeek and XmlPoke tasks have been added to .NET Framework 4.0. However, when I tried the following:

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <Target Name="XmlPokeTest">
    <XmlPoke etc.../>
  </Target>
</Project>

... I get the dreaded task was not found message:

Microsoft (R) Build Engine Version 4.0.30319.1 Copyright (C) Microsoft Corporation 2007. All rights reserved. error MSB4036: The "XmlPoke" task was not found.

The error has a standard set of suggested solutions, including this one:

Check the following:
3.) The task is correctly declared within the project file,
or in the *.tasks files located in the
"C:\Windows\Microsoft.NET\Framework\v2.0.50727" directory.

This works:

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <UsingTask TaskName="Microsoft.Build.Tasks.XmlPoke"
             AssemblyName="Microsoft.Build.Tasks.v4.0, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"/>
  <Target Name="XmlPokeTest">
    <XmlPoke etc.../>
  </Target>
</Project>

There is a Microsoft.Commmon.Tasks file in the C:\Windows\Microsoft.NET\Framework\v4.0.30319 folder that lists the new MSBuild 4.0 tasks, like XmlPeek and XmlPoke. But MSBuild 4.0 is apparently still using the Microsoft.Commmon.Tasks file in C:\Windows\Microsoft.NET\Framework\v2.0.50727.

Using the toolsversion switch also works, presumably causing MSBuild to reference the new 4.0 Microsoft.Common.Tasks file:

msbuild /toolsversion:4.0 XmlPokeTest.proj

For future reference, the 4.0 Microsoft.Common.Tasks file includes these entries that are not included in the the 2.0 version:

AssignProjectConfiguration
AssignTargetPath
CreateCSharpManifestResourceName
CreateVisualBasicManifestResourceName
FindAppConfigFile
FindInList
FormatUrl
FormatVersion
GenerateTrustInfo
GetReferenceAssemblyPaths
Move
RequiresFramework35SP1Assembly
ResolveManifestFiles
ResolveNonMSBuildProjectOutput
UpdateManifest
XmlPeek
XmlPoke
XslTransformation