Bart De Smet recently posted a blog entry showing to invoke PowerShell script from within MSBuild with 45 lines of C# !!!  Check it out HERE.

Jeffrey Snover [MSFT]
Windows Management Partner Architect
Visit the Windows PowerShell Team blog at:    http://blogs.msdn.com/PowerShell
Visit the Windows PowerShell ScriptCenter at:  http://www.microsoft.com/technet/scriptcenter/hubs/msh.mspx