C#

System.Diagnostics.Process.Start("regsvr32.exe", 
    string.Format("/s \"{0}\"", Path To Dll or OCX))

[System.Runtime.InteropServices.DllImport("Dll or OCX name", EntryPoint="DllRegisterServer")]
static extern int RegisterMyDll();

using System;
using System.Runtime.InteropServices;
 
class ComUtils
{
    [DllImport("kernel32.dll")]
    private static extern IntPtr LoadLibrary(string fileName);
    
    [DllImport("kernel32.dll")]
    private static extern int FreeLibrary(IntPtr hModule);
    
    [DllImport("kernel32.dll")]
    private static extern IntPtr GetProcAddress(IntPtr hModule, string lpProcName);
    
    [DllImport("user32.dll")]
    private static extern int CallWindowProc(
        IntPtr lpPrevWndFunction, 
        int hWnd, int msg, int wParam, int lParam);
    
    public static bool RegisterServer(string path)
    {
        IntPtr hModule = LoadLibrary(path);
        if (IntPtr.Zero == hModule)
        {
            // Failed to load
            return false;
        }
        
        try
        {
            IntPtr register = GetProcAddress(hModule, "DllRegisterServer");
            if (IntPtr.Zero == register)
            {
                // Failed to find entry-point
                return false;
            }
            else
            {
                int ret = CallWindowProc(register, 0, 0, 0, 0);
                	
                if (0 == ret) return true;
                else return false;
            }
        }
        finally
        {
            FreeLibrary(hModule);
        }
    }
}

using (DirectoryEntry de = new DirectoryEntry())
{            
de.Path = "LDAP://celticrain/OU=Wrox Press, DC=eichkogelstrasse, DC=local";
DirectoryEntries users = de.Children;

DirectoryEntry user = users.Add("CN=John Doe", "user");
user.Properties["company"].Add("Some Company");
user.Properties["department"].Add("Sales");
user.Properties["employeeID"].Add("4711");
user.Properties["samAccountName"].Add("JDoe");
user.Properties["userPrincipalName"].Add("JDoe@eichkogelstrasse.local");
user.Properties["sn"].Add("Doe");
user.Properties["givenName"].Add("John");
user.Properties["userPassword"].Add("someSecret");
user.CommitChanges();
}

using (DirectoryEntry de = new DirectoryEntry())
{
de.Path = "LDAP://celticrain/CN=John Doe, CN=Users, DC=eichkogelstrasse, DC=local";
de.Invoke("SetPassword", "anotherSecret");
de.CommitChanges();
ActiveDs.IADsUser user = (ActiveDs.IADsUser)de.NativeObject;
user.SetPassword("someSecret");
user.AccountDisabled = false;
de.CommitChanges();
}

• Make sure you're not using Unicode methods without the Unicode layer for Win9x
  
• Make sure you're not using methods that only work on Windows NT (such as the Network Management API or the GINA methods)
  
• If you do use Unicode, make sure you make two builds: 1 for ANSI and 1 for Unicode. Make sure you install the appropriate build on the appropriate platform.