_Minify.props.xml

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">

  <!-- CSS Files to Minify -->
  <ItemGroup>
    <CssFiles Include="css\reset.css" />
    <CssFiles Include="css\layout.css" />
  </ItemGroup>
  
 </Project>

Minify.tasks.xml

<?xml version="1.0" encoding="utf-8"?>
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  
  <!--
    This task will minify CSS and JS files.
    By default it was process 'all' files inside the specified directories
    Depends on the YUI Compressor DLL, located in the Tools folder (http://yuicompressor.codeplex.com/documentation)

    VISUAL STUDIO : update your projects .ProjectName.Targets file to Import the project
    
    <Import Project="../Build/Minify.tasks"/>
    and get the task hooked into   
    <Target Name="BeforeBuild" DependsOnTargets="Minify">
    
    It is possible to define the order and which files you want to minify, to do this create
    a _Minify.props file, this can be global, or inside your Js and Css scripts folder.
  -->

  <UsingTask TaskName="CssCompressorTask" AssemblyFile="..\Tools\YUI\Yahoo.Yui.Compressor.Build.MsBuild.dll" />
  <UsingTask TaskName="JavaScriptCompressorTask" AssemblyFile="..\Tools\YUI\Yahoo.Yui.Compressor.Build.MsBuild.dll" />
  
  <!-- Configuration -->
  <PropertyGroup>
    <!-- Folders to deal with -->
    <CssFolder>Css</CssFolder>
    <JsFolder>Scripts</JsFolder>
    <!-- Where _Manifest.props file *could* be -->
    <CssManifest>$(MSBuildProjectDirectory)\$(CssFolder)\_Minify.props</CssManifest>
    <JsManifest>$(MSBuildProjectDirectory)\$(JsFolder)\_Minify.props</JsManifest>
    <!-- Output -->
    <MinifyCssOutput>$(CssFolder)\minified.css</MinifyCssOutput>
    <MinifyJsOutput>$(JsFolder)\minified.js</MinifyJsOutput>
  </PropertyGroup>

  <!-- Import Everything, but don't import the output -->
  <ItemGroup>
    <CssFiles Include="$(CssFolder)\*.css" Exclude="$(MinifyCssOutput)" Condition="!Exists($(CssManifest))" />
    <JsFiles Include="$(JsFolder)\*.js" Exclude="$(MinifyJsOutput)" Condition="!Exists($(JsManifest))" />
  </ItemGroup>
  
  <!-- If a _Manifest.props file exists, import it (overrides above) -->
  <Import Project="$(CssManifest)" Condition="Exists($(CssManifest))" />
  <Import Project="$(JsManifest)" Condition="Exists($(JsManifest))"/>

  <!-- Do something! -->
  <Target Name="Minify">
    <Message Text="Compressing..."/>

    <Message Text="ALL $(CssFolder)\**\*.css files" Condition="!Exists($(CssManifest))" />
    <Message Text="ALL $(JsFolder)\**\*.js files" Condition="!Exists($(JsManifest))" />

    <Message Text="CSS files from Manifest | $(CssManifest)" Condition="Exists($(CssManifest))" />
    <Message Text="JS files from Manifest | $(JsManifest)" Condition="Exists($(JsManifest))" />
    
    <!-- Do compression -->
    <CssCompressorTask
       SourceFiles="@(CssFiles)"
       DeleteSourceFiles="false"
       OutputFile="$(MinifyCssOutput)"
       CompressionType="Standard"
       LoggingType="Info"
       PreserveComments="false"
       LineBreakPosition="-1"
     />

    <JavaScriptCompressorTask
        SourceFiles="@(JsFiles)"
       DeleteSourceFiles="false"
       OutputFile="$(MinifyJsOutput)"
       CompressionType="Standard"
       LoggingType="Info"
       LineBreakPosition="-1"
     />

  </Target>
  
</Project>