C#

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.DirectoryServices;
using System.DirectoryServices.ActiveDirectory;
using System.Data;
using System.IO;
using System.Xml;

namespace FindAdmins
{
    class Program
    {
        static void Main(string[] args)
        {
            //Setup the LDAP connection to the domain your user is part of.
            string connectionPrefix = "LDAP://" + FriendlyDomainToLdapDomain(Environment.UserDomainName);
            DirectoryEntry entry = new DirectoryEntry(connectionPrefix);
            DirectorySearcher mySearcher = new DirectorySearcher(entry);
            //Find only computers
            mySearcher.Filter = "(objectClass=computer)";
            //Performance tweaks
            mySearcher.PageSize = 50000;
            mySearcher.SizeLimit = 100000;
            mySearcher.Asynchronous = true;
            //Only want common name
            mySearcher.PropertiesToLoad.Add("cn");
            //Find everything
            SearchResultCollection results = mySearcher.FindAll();
            Console.WriteLine("Number of machines found: " + results.Count);
            int count = 0;

            //DataTable for results
            DataTable table = new DataTable();
            table.TableName = Environment.UserDomainName;
            table.Columns.Add("Machine");
            table.Columns.Add("Group");
            table.Columns.Add("User");

            //Since we have all machines in the domain we loop over them
            foreach (SearchResult result in results)
            {
                //DirectoryEntry direntry = new DirectoryEntry(result.Path);

                //Tracking progress
                count++;
                Console.Write(count + "\r");
                
                try
                {
                    //Connect directly to the machine.
                    DirectoryEntry remMachine = new DirectoryEntry("WinNT://" + result.Properties["cn"][0].ToString() + ",Computer");
                    
                    //Read the members of "Administrators" local group
                    DirectoryEntry admGroup = remMachine.Children.Find("administrators", "group");
                    object members = admGroup.Invoke("members", null);

                    //Loop over the members and see if they are a group themselves.
                    foreach (object groupMember in (IEnumerable)members)
                    {
                        DirectoryEntry member = new DirectoryEntry(groupMember);
                        //If it's a group, get the members.
                        if (member.SchemaClassName == "Group")
                        {
                            object admMembers = member.Invoke("members", null);
                            foreach (object admMember in (IEnumerable)admMembers)
                            {
                                DirectoryEntry membername = new DirectoryEntry(admMember);
                                DataRow dr = table.NewRow();
                                dr["Machine"] = remMachine.Name.ToString();
                                dr["Group"] = member.Name.ToString();
                                dr["User"] = membername.Name.ToString();
                                table.Rows.Add(dr);
                                membername.Dispose();
                            }
                        }
                        //Just a user, write it down
                        else if (member.SchemaClassName == "User")
                        {
                            DataRow dr = table.NewRow();
                            dr["Machine"] = remMachine.Name.ToString();
                            dr["Group"] = "Administrators";
                            dr["User"] = member.Name.ToString();
                            table.Rows.Add(dr);
                            member.Dispose();
                        }
                    }
                    admGroup.Dispose();
                    //member.Close();
                    remMachine.Dispose();
                    GC.Collect();
                }
                catch (Exception e)
                {
                    //writer.WriteLine("  " + e.Message);
                }
                //direntry.Close();
            }
            //table.WriteXml(@"C:\admins.xml", XmlWriteMode.WriteSchema, true);
            table.WriteXml(@"C:\admins.xml", true);
            //table.WriteXmlSchema(@"C:\admins.xsd", true);
            mySearcher.Dispose();
            entry.Dispose();
        }

        //Find the LDAP domain given the NT domain of the user running the tool
        public static string FriendlyDomainToLdapDomain(string friendlyDomainName)
        {
            string ldapPath = null;
            try
            {
                DirectoryContext objContext = new DirectoryContext(DirectoryContextType.Domain, friendlyDomainName);
                Domain objDomain = Domain.GetDomain(objContext);
                ldapPath = objDomain.Name;
            }
            catch (DirectoryServicesCOMException e)
            {
                ldapPath = e.Message.ToString();
            }
            return ldapPath;
        }
    }
}