here is the code for a very small little utility that might get you on your way:
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
Public Function BroadcastMessage(sToUser As String, _
sMessage As String) As Boolean
Dim yToName() As Byte
Dim yMsg() As Byte
yToName = sToUser & 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 cmdSend_Click()
Dim blnSend As Boolean
blnSend = BroadcastMessage(Trim(txtSendTo.Text), Trim(txtToSend.Text))
txtSendTo.Text = ""
txtToSend.Text = ""
txtSendTo.SetFocus
End Sub