The HP TRIM SDK isn't registered in the GAC when TRIM is installed, so you need to add it to the 'PATH' environment variable before you can use it. Here's a simple console app that shows how I do it.

InitialisingTrim.cs

using Microsoft.Win32;
using System;

namespace TrimDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            //The TRIM SDK isn't registered in the GAC when TRIM is installed, 
            //so you need to add it to the 'PATH' environment variable
            InitialiseTrim();

            //For some reason unbeknownst to me, you still can't use the TRIM SDK from 
            //within this method, you need to do it from within another method, like this one...
            BootstrapApp();
        }

        static void InitialiseTrim()
        {
            //Get the TRIM installation directory from the registry 
            var trimPath = Registry.LocalMachine.GetValue(
                @"SOFTWARE\Hewlett-Packard\HP TRIM\MSISettings\INSTALLDIR",
                @"C:\Program Files\Hewlett-Packard\HP TRIM\");

            //And add it to the 'PATH' environment variable in 
            Environment.SetEnvironmentVariable("PATH",
                string.Format("{0};{1}", Environment.GetEnvironmentVariable("PATH"), trimPath),
                EnvironmentVariableTarget.Process);
        }

        static void BootstrapApp()
        {
            //You can happily access TRIM from here.
        }
    }
}