Urgent!! How to login via web serivices

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webservice

I wish to do my system login by using web services.

May i know how to do it?

Please provide example source code for web services and how to call it in asp.net.

Thanks!!!!!

[Edit]
Moved here on OP's behalf from non-answer

I have tried it but have problem. i dun know what is the error occur. Hope have some one willing help me solve this problem.
This is my web method in web services.when i invoke this web method, i return the value 0 and show me the error message although i key in the correct username and password.

Public Function Login(ByVal username As String, ByVal password As String) As String()
    Dim data(3) As String
    ' success = New String() {"3"}
    Dim validID As Integer

    Dim cmd As New SqlCommand

    DBStudent.Open()
    cmd.CommandText = "SELECT username,studentPass,studentEmel FROM student"
    cmd.Connection = DBStudent

    Dim myDataReader As SqlDataReader
    myDataReader = cmd.ExecuteReader

    While myDataReader.Read
        If username = myDataReader("username".ToString) And password = myDataReader("studentPass".ToString) Then
            data(0) = 1
            data(1) = myDataReader("username".ToString)
            data(2) = myDataReader("studentPass".ToString)
            data(3) = myDataReader("studentEmel".ToString)
            validID = 1
            Exit While
        Else
            data(0) = 0
        End If

    End While

    myDataReader.Close()
    cmd.Dispose()


    If validID <> 1 Then
        MsgBox(vbTab + vbTab + "Login fail." + vbCrLf + vbCrLf + "Invalid User", MsgBoxStyle.Exclamation + MsgBoxStyle.OkOnly, "Status Login")

    End If
    DBSpin.Close()

    Return data


End Function

[/Edit]