CreateSaferProcess(@"calc.exe","",SaferLevel.NormalUser);

//http://odetocode.com/Blogs/scott/archive/2004/10/28/602.aspx
public static void CreateSaferProcess(String fileName,String arguments,SaferLevel saferLevel)
{
   IntPtr saferLevelHandle = IntPtr.Zero;

   //Create a SaferLevel handle to match what was requested
   if (!WinSafer.SaferCreateLevel(
         SaferLevelScope.User,saferLevel,SaferOpen.Open,out saferLevelHandle,IntPtr.Zero))
   {
      throw new Win32Exception(Marshal.GetLastWin32Error());
   }
   try
   {
      //Generate the access token to use,based on the safer level handle.
      IntPtr hToken = IntPtr.Zero;

      if (!WinSafer.SaferComputeTokenFromLevel(
            saferLevelHandle,// SAFER Level handle
            IntPtr.Zero,// NULL is current thread token.
            out hToken,// Target token
            SaferTokenBehavIoUr.Default,// No flags
            IntPtr.Zero))      // Reserved
      {
         throw new Win32Exception(Marshal.GetLastWin32Error());
      }
      try
      {
         //Now that we have a security token,we can lauch the process
         //using the standard CreateProcessAsUser API
         STARTUPINFO si = new STARTUPINFO();
         si.cb = Marshal.SizeOf(si);
         si.lpDesktop = String.Empty;

         PROCESS_INFORMATION pi = new PROCESS_INFORMATION();

         // Spin up the new process
         Boolean bResult = Windows.CreateProcessAsUser(
               hToken,fileName,arguments,IntPtr.Zero,//process attributes
               IntPtr.Zero,//thread attributes
               false,//inherit handles
               0,//CREATE_NEW_CONSOLE
               IntPtr.Zero,//environment
               null,//current directory
               ref si,//startup info
               out pi); //process info

         if (!bResult)
            throw new Win32Exception(Marshal.GetLastWin32Error());

         if (pi.hProcess != IntPtr.Zero)
            Windows.CloseHandle(pi.hProcess);

         if (pi.hThread != IntPtr.Zero)
            Windows.CloseHandle(pi.hThread);
      }
      finally
      {
         if (hToken != IntPtr.Zero)
            Windows.CloseHandle(hToken);
      }
   }
   finally
   {
      WinSafer.SaferCloseLevel(saferLevelHandle);
   }
}

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;

namespace PInvoke
{
   public class WinSafer
   {
      /// <summary>
      /// The SaferCreateLevel function opens a SAFER_LEVEL_HANDLE.
      /// </summary>
      /// <param name="scopeId">The scope of the level to be created.</param>
      /// <param name="levelId">The level of the handle to be opened.</param>
      /// <param name="openFlags">Must be SaferOpenFlags.Open</param>
      /// <param name="levelHandle">The returned SAFER_LEVEL_HANDLE. When you have finished using the handle,release it by calling the SaferCloseLevel function.</param>
      /// <param name="reserved">This parameter is reserved for future use. IntPtr.Zero</param>
      /// <returns></returns>
      [DllImport("advapi32",SetLastError = true,CallingConvention = CallingConvention.StdCall)]
      public static extern bool SaferCreateLevel(SaferLevelScope scopeId,SaferLevel levelId,SaferOpen openFlags,out IntPtr levelHandle,IntPtr reserved);

      /// <summary>
      /// The SaferComputeTokenFromLevel function restricts a token using restrictions specified by a SAFER_LEVEL_HANDLE.
      /// </summary>
      /// <param name="levelHandle">SAFER_LEVEL_HANDLE that contains the restrictions to place on the input token. Do not pass handles with a LevelId of SAFER_LEVELID_FULLYTRUSTED or SAFER_LEVELID_DISALLOWED to this function. This is because SAFER_LEVELID_FULLYTRUSTED is unrestricted and SAFER_LEVELID_DISALLOWED does not contain a token.</param>
      /// <param name="inAccessToken">Token to be restricted. If this parameter is NULL,the token of the current thread will be used. If the current thread does not contain a token,the token of the current process is used.</param>
      /// <param name="outAccessToken">The resulting restricted token.</param>
      /// <param name="flags">Specifies the behavior of the method.</param>
      /// <param name="lpReserved">Reserved for future use. This parameter should be set to IntPtr.EmptyParam.</param>
      /// <returns></returns>
      [DllImport("advapi32",CallingConvention = CallingConvention.StdCall)]
      public static extern bool SaferComputeTokenFromLevel(IntPtr levelHandle,IntPtr inAccessToken,out IntPtr outAccessToken,SaferTokenBehavIoUr flags,IntPtr lpReserved);

      /// <summary>
      /// The SaferCloseLevel function closes a SAFER_LEVEL_HANDLE that was opened by using the SaferIdentifyLevel function or the SaferCreateLevel function.</summary>
      /// <param name="levelHandle">The SAFER_LEVEL_HANDLE to be closed.</param>
      /// <returns>TRUE if the function succeeds; otherwise,FALSE. For extended error information,call GetLastWin32Error.</returns>
      [DllImport("advapi32",CallingConvention = CallingConvention.StdCall)]
      public static extern bool SaferCloseLevel(IntPtr levelHandle);
   } //class WinSafer

   /// <summary>
   /// Specifies the behavIoUr of the SaferComputeTokenFromLevel method
   /// </summary>
   public enum SaferTokenBehavIoUr : uint
   {
      /// <summary></summary>
      Default = 0x0,/// <summary>If the OutAccessToken parameter is not more restrictive than the InAccessToken parameter,the OutAccessToken parameter returns NULL.</summary>
      NullIfEqual = 0x1,/// <summary></summary>
      CompareOnly = 0x2,/// <summary></summary>
      MakeInert = 0x4,/// <summary></summary>
      WantFlags = 0x8
   }

   /// <summary>
   /// The level of the handle to be opened.
   /// </summary>
   public enum SaferLevel : uint
   {
      /// <summary>Software will not run,regardless of the user rights of the user.</summary>
      Disallowed = 0,/// <summary>Allows programs to execute with access only to resources granted to open well-known groups,blocking access to Administrator and Power User privileges and personally granted rights.</summary>
      Untrusted = 0x1000,/// <summary>Software cannot access certain resources,such as cryptographic keys and credentials,regardless of the user rights of the user.</summary>
      Constrained = 0x10000,/// <summary>Allows programs to execute as a user that does not have Administrator or Power User user rights. Software can access resources accessible by normal users.</summary>
      NormalUser = 0x20000,/// <summary>Software user rights are determined by the user rights of the user.</summary>
      FullyTrusted = 0x40000
   }

   /// <summary>
   /// The scope of the level to be created.
   /// </summary>
   public enum SaferLevelScope : uint
   {
      /// <summary>The created level is scoped by computer.</summary>
      Machine = 1,/// <summary>The created level is scoped by user.</summary>
      User = 2
   }

   public enum SaferOpen : uint
   {
      Open = 1
   }
} //namespace PInvoke