1. Download MSBuild Community Task
2. Add the following to the .csproj file of the project you want to follow the svn build numbering. Add just before </Project>

  <!-- Import of the MSBuildCommunityTask targets -->
<Import Project="$(MSBuildExtensionsPath)\MSBuildCommunityTasks\MSBuild.Community.Tasks.Targets" />

<!-- to manage version number -->
<Target Name="Version">
  <Version VersionFile="version.txt" RevisionType="Increment">
    <Output TaskParameter="Major" PropertyName="Major" />
    <Output TaskParameter="Minor" PropertyName="Minor" />
    <Output TaskParameter="Build" PropertyName="Build" />
    <Output TaskParameter="Revision" PropertyName="Revision" />
  </Version>
</Target>

  <!-- to generate our personnal version info -->
  <Target Name="AssemblyInfo">

  <SvnVersion LocalPath="$(MSBuildProjectDirectory)" Condition="Exists('$(ProgramFiles)\subversion\bin\svn.exe')">
    <Output TaskParameter="Revision" PropertyName="Build" />
  </SvnVersion> 

  <AssemblyInfo
    CodeLanguage="CS"
    OutputFile="Properties\AssemblyInfo.cs"
    AssemblyTitle="WindScanner"
    AssemblyDescription=""
    AssemblyCompany="Risø"
    AssemblyProduct="windscanner"
    AssemblyCopyright="Copyright © 2010"
    ComVisible="false"
    Guid="88812638-9547-4480-3bf4-4fe25103b35c"
    AssemblyVersion="$(Major).$(Minor).$(Build).$(Revision)"
    AssemblyFileVersion="$(Major).$(Minor).$(Build).$(Revision)"
    Condition="$(Revision) != '0' "/>
</Target>

<!-- We launch these two targets -->
<Target Name="BeforeBuild">
    <CallTarget Targets="Version" />
    <CallTarget Targets="AssemblyInfo" />
</Target>

<Target Name="AfterBuild">
</Target>

Change the path of your svn installation if necessary.

You can now use stuff like

public static String Version
        {
            get
            {
                return System.Reflection.Assembly.GetExecutingAssembly().GetName().Version.ToString();
            }
        }

And the the changes reflecting the svn build!