public enum NERR
        {
            NERR_Success = 0,
            ERROR_ACCES_DENIED = 5,
            ERROR_NOT_ENOUGH_MEMORY = 8,
            ERROR_MORE_DATA = 234,
            ERROR_BAD_NET_PATH = 53,
            ERROR_NO_NETWORK = 1222,
            ERROR_NO_BROWSER_SERVER_FOUND = 6118
        }

        public enum PLATFORM_ID : uint
        {
            PLATFORM_ID_DOS = 300,
            PLATFORM_ID_OS2 = 400,
            PLATFORM_ID_NT = 500,
            PLATFORM_ID_OSF = 600,
            PLATFORM_ID_WMS = 700
        }

        [DllImport("netapi32.dll", EntryPoint = "NetServerEnum")]
        public static extern NERR NetServerEnum(
            [MarshalAs(UnmanagedType.LPWStr)] string ServerName, int Level, out IntPtr BufPtr,
            int PrefMaxLen, ref int EntriesRead, ref int TotalEntries, uint ServetType,
            [MarshalAs(UnmanagedType.LPWStr)] string Domain, int ResumeHandle);

        [DllImport("netapi32.dll", EntryPoint = "NetApiBufferFree")]
        public static extern NERR NetApiBufferFree(IntPtr Buffer);

        const uint SV_TYPE_SQLSERVER = 0x00000004;

        [StructLayout(LayoutKind.Sequential)]
        public struct SERVER_INFO_101
        {
            [MarshalAs(UnmanagedType.U4)]
            public uint sv101_platform_id;

            [MarshalAs(UnmanagedType.LPWStr)]
            public string sc101_name;

            [MarshalAs(UnmanagedType.U4)]
            public uint sc101_version_major;

            [MarshalAs(UnmanagedType.U4)]
            public uint sv101_type;

            [MarshalAs(UnmanagedType.LPWStr)]
            public string sv101_comment;
        }

        public static List<string> GetSQLServerList()
        {
            SERVER_INFO_101 si;
            IntPtr pInfo = IntPtr.Zero;
            int entriesread = 0;
            int totalentries = 0;
            List<string> srvs = new List<string>();

            try
            {
                NERR err = NetServerEnum(null, 101, out pInfo, -1, ref entriesread,
                    ref totalentries, SV_TYPE_SQLSERVER, null, 0);

                if ((err == NERR.NERR_Success || err == NERR.ERROR_MORE_DATA) && pInfo != IntPtr.Zero)
                {
                    int ptr = pInfo.ToInt32();

                    for (int i = 0; i < entriesread; i++)
                    {
                        si = (SERVER_INFO_101)Marshal.PtrToStructure(new IntPtr(ptr), typeof(SERVER_INFO_101));
                        srvs.Add(si.sc101_name);
                        ptr += Marshal.SizeOf(si);
                    }
                }
            }
            catch { }
            finally
            {
                if (pInfo != IntPtr.Zero)
                    NetApiBufferFree(pInfo);
            }
            return srvs;
        }

        private void bRegresh_Click(object sender, EventArgs e)
        {
            cbSrv.DataSource = GetSQLServerList();
        }
    }

DataTable srv = SqlDataSourceEnumerator.Instance.GetDataSources();