WinPopup compatible instant messenger for corporate networks

How to realize this function? like Bopup Messenger or winpopup?
Bopup Messenger detail:
Bopup Messenger is an Award-Winning instant messenger that enables you to communicate with other users connected across the same LAN, similar to WinPopup and net send.

Improved mechanism of sending messages makes messaging faster and at the same time economically uses system memory and resources of a computer.

The program features an intuitive interface offering an easy-to-use, clear menu and multilingual support. In addition to basic communication options, Bopup Messenger also offers you more features and functions.
http://www.blabsoft.com/products/messenger/

I find a way to do it!
Send a message in a WinPopup format to a computer on the network:
Private Declare Function NetMessageBufferSend Lib _
"NETAPI32.DLL" (yServer As Any, yToName As Byte, _
yFromName As Any, yMsg As Byte, ByVal lSize As Long) As Long

Private Const NERR_Success As Long = 0&


Public Function BroadcastMessage(sToUser As String, _
sFromUser As String, sMessage As String) As Boolean

Dim yToName() As Byte
Dim yFromName() As Byte
Dim yMsg() As Byte
Dim l As Long

yToName = sToUser & vbNullChar
yFromName = sFromUser & vbNullChar
yMsg = sMessage & vbNullChar

If NetMessageBufferSend(ByVal 0&, yToName(0), ByVal 0&, _
yMsg(0), UBound(yMsg)) = NERR_Success Then

BroadcastMessage = True

End If

End Function

Private Sub Command1_Click()
Dim x As Boolean

x = BroadcastMessage(TxtTo.Text, TxtFrom.Text, TxtMsg.Text)
If x Then
MsgBox "Message Sent"
Else
MsgBox "Message Not Sent"
End If

End Sub


But i can't send any message! any one can help me!?

I use the winapi function:
"NetMessageBufferSend" to realize it!
Pay Attention to: you must open Messager Service!

Module1:
Option Explicit

Private Declare Function NetMessageBufferSend Lib "netapi32.dll" _
(ByVal servername As String, _
ByVal msgname As String, _
ByVal fromname As String, _
ByVal Buffer As String, _
ByVal BufSize As Long) As Long

Private Const NERR_SUCCESS As Long = 0
Private Const NERR_BASE As Long = 2100
Private Const NERR_NetworkError As Long = (NERR_BASE + 36)
Private Const NERR_NameNotFound As Long = (NERR_BASE + 173)
Private Const NERR_UseNotFound As Long = (NERR_BASE + 150)
Private Const ERROR_ACCESS_DENIED As Long = 5
Private Const ERROR_BAD_NETPATH As Long = 53
Private Const ERROR_NOT_SUPPORTED As Long = 50
Private Const ERROR_INVALID_PARAMETER As Long = 87
Private Const ERROR_INVALID_NAME As Long = 123


Public Function NetSendMessage(ByVal sSendTo As String, ByVal sMessage As String) As Long
Dim ret As Long

'conversion of strings
sSendTo = StrConv(sSendTo, vbUnicode)
sMessage = StrConv(sMessage, vbUnicode)
'transmitting message to net comp.
NetSendMessage = NetMessageBufferSend(vbNullString, sSendTo, vbNullString, _
sMessage, Len(sMessage))
End Function

'desc. of api err.
Public Function NetSendErrorMessage(ErrNum As Long) As String
Select Case ErrNum
Case NERR_SUCCESS
NetSendErrorMessage = "The message was successfully sent"
Case NERR_NameNotFound
NetSendErrorMessage = "Send To not found"
Case NERR_NetworkError
NetSendErrorMessage = "General network error occurred"
Case NERR_UseNotFound
NetSendErrorMessage = "Network connection not found"
Case ERROR_ACCESS_DENIED
NetSendErrorMessage = "Access to computer denied"
Case ERROR_BAD_NETPATH
NetSendErrorMessage = "Sent From server name not found."
Case ERROR_INVALID_PARAMETER
NetSendErrorMessage = "Invalid parameter(s) specified."
Case ERROR_NOT_SUPPORTED
NetSendErrorMessage = "Network request not supported."
Case ERROR_INVALID_NAME
NetSendErrorMessage = "Illegal character or malformed name."
Case Else
NetSendErrorMessage = "Unknown error executing command."
End Select
End Function

Form1:
Private Sub Command1_Click()
Dim ret As Long

ret = NetSendMessage(Text1.Text, Text2.Text)
If ret <> 0 Then
MsgBox NetSendErrorMessage(ret), vbCritical, "Error"
Else
MsgBox NetSendErrorMessage(ret), vbInformation, "NetSend"
End If
End Sub