Here is a code snippet that demonstrates how to get list of user accounts on your windows machine using .Net. Since there are no native .Net APIs to accomplish this task, you will need to use Interop to use Win32 APIs related to user management.

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

namespace UserEnvironment
{
 class Program
 {
  static void Main(string[] args)
  {
   Console.WriteLine(Environment.OSVersion.VersionString);
   Console.WriteLine("OS: {0}.{1}", 
    Environment.OSVersion.Version.Major, 
    Environment.OSVersion.Version.Minor);
   Console.WriteLine("****************************************");
   var accounts = GetListOfAccounts();
   if (accounts.Count != 0)
   {
    Console.WriteLine("User accounts on " + 
     System.Environment.MachineName + System.Environment.NewLine);
    foreach (var account in accounts)
    {
     Console.WriteLine(account);
    }
   }
   else
   {
    Console.WriteLine("No user account found!");
   }
  }

  static System.Collections.Specialized.StringCollection GetListOfAccounts()
  {
   int resumeHandle;
   int entriesRead;
   int totalEntries;
   IntPtr bufPtr;

   var userAccounts = new System.Collections.Specialized.StringCollection();
   NetUserWin32.NetUserEnum(null, 0, 2, out bufPtr, -1, 
    out entriesRead, out totalEntries, out resumeHandle);
   if (entriesRead > 0)
   {
    var users = new NetUserWin32.USER_INFO_0[entriesRead];
    IntPtr iter = bufPtr;
    for (int i = 0; i < entriesRead; i++)
    {
     users[i] = (NetUserWin32.USER_INFO_0)Marshal.PtrToStructure(iter, 
                           typeof(NetUserWin32.USER_INFO_0));
     iter = (IntPtr)((int)iter + Marshal.SizeOf(typeof(NetUserWin32.USER_INFO_0)));
     userAccounts.Add(users[i].Username);
    }
    NetUserWin32.NetApiBufferFree(bufPtr);
   }
   return userAccounts;
  }
 }
}

namespace UserEnvironment
{
 public class NetUserWin32
 {
  [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Unicode)]
  public struct USER_INFO_0
  {
   public String Username;
  }

  [DllImport("Netapi32.dll")]
  public extern static int NetUserEnum([MarshalAs(UnmanagedType.LPWStr)]string servername, 
    int level, int filter, out IntPtr bufptr, 
    int prefmaxlen, out int entriesread, out int totalentries,
    out int resume_handle);

  [DllImport("Netapi32.dll")]
  public extern static int NetApiBufferFree(IntPtr Buffer);
	}
}

As i was building a new desktop application for Windows7, I was adding support to detect if user's operating system was Windows 7 or not. So I fired up handy Win32 API GetVersionEx. I don't know for some reason I was hoping to see a major version number revision to 7 for Windows 7 release. Well, it was not. There is only a minor version number increment to 1 from 0 that was used for Vista. So you will see that for Windows 7, major version number is still 6. You can see it from the debugger screen shot of my little application.

I guess this falls in line with what most people have been saying that Windows 7 is not a major change in windows operating system but it is a better version of Windows Vista. I guess after looking at these numbers of dwMajorVersion and dwMinorVersion, MS has also indicating that Windows 7 is not a major release for operating system.