The most complex part with TP services is authentication. It is recommended to create TpPolicy class and use it for authentication. Just copy the complete class code below.

using Microsoft.Web.Services3;
using Microsoft.Web.Services3.Design;
using Microsoft.Web.Services3.Security;
using Microsoft.Web.Services3.Security.Tokens;

namespace TpIntegration
{
   public class TpPolicy : Policy
   {
      public TpPolicy()
      {
         Assertions.Add(new UsernameOverTransportAssertion());
      }

      public static UsernameToken GetUsernameToken(string username, string password, PasswordOption passwordOption)
      {
         UsernameToken token = new UsernameToken(username, password, passwordOption);

         ISecurityTokenManager securityTokenManager =
            SecurityTokenManager.GetSecurityTokenManagerByTokenType(WSTrust.TokenTypes.UsernameToken);
         securityTokenManager.CacheSecurityToken(token);

         return token;
      }

      public static void ApplyAutheticationTicket(WebServicesClientProtocol protocol, string userName, string password)
      {
         UsernameToken token = GetUsernameToken(userName, password, PasswordOption.SendPlainText);
         protocol.SetClientCredential(token);
         protocol.SetPolicy(new TpPolicy());
      }
   }
}

Now we are ready to investigate power of TargetProcess web services API.

using System;
using TpIntegration.UserService;

namespace TpIntegration
{
   internal class Program
   {
      private static void Main(string[] args)
      {
         // Create web service and path authentication.
         // "admin" / "admin" is login/password of user
         // that has access to TargetProcess
         UserServiceWse userService = new UserServiceWse();
         TpPolicy.ApplyAutheticationTicket(userService, "admin", "admin");

         // Retrieve all users in TargetProcess
         UserDTO[] users = userService.RetrieveAll();

         // Make something interesting with users list.
         // For example, just show users
         foreach (UserDTO user in users)
         {
            Console.WriteLine(user.FirstName + " " + user.LastName);
         }
      }
   }
}