okay, finally got it, this was a huge pain and here's the post that started it all because i actually thought my linq to sql was off when it turned out to be entirely different.

definitely check the last entry of this post here:

http://www.vbforums.com/showthread.php?t=620770

as for the code required, included below is the client side codebehind:

Code:
Imports System.ServiceModel.DomainServices.Client
Imports EstimatorSilverlight.Web

Partial Public Class MainPage
    Inherits UserControl
    Dim context = New LoginContext()
    Dim invokeop As InvokeOperation(Of Integer)

    Public Sub New()
        InitializeComponent()
    End Sub

    Private Sub btnLogin_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btnLogin.Click
        Dim username As String = tbUserName.Text
        Dim password As String = pbPassword.Password

        invokeop = context.countloginsmatching(username, password)
        AddHandler invokeop.Completed, AddressOf invokeOperation_Completed

    End Sub

    Private Sub invokeOperation_Completed(ByVal Sender As Object, ByVal E As EventArgs)
        Label3.Content = invokeop.Value
    End Sub

    Private Sub LoginDomainDataSource_LoadedData(ByVal sender As System.Object, ByVal e As System.Windows.Controls.LoadedDataEventArgs) Handles LoginDomainDataSource.LoadedData

        If e.HasError Then
            System.Windows.MessageBox.Show(e.Error.ToString, "Load Error", System.Windows.MessageBoxButton.OK)
            e.MarkErrorAsHandled()
        End If
    End Sub
End Class
and then finally the domainservice code as well - the key is the final function and the invoke tag:

Code:
Option Compare Binary
Option Infer On
Option Strict On
Option Explicit On

Imports EstimatorSilverlight.Web
Imports System
Imports System.Collections.Generic
Imports System.ComponentModel
Imports System.ComponentModel.DataAnnotations
Imports System.Data
Imports System.Linq
Imports System.ServiceModel.DomainServices.EntityFramework
Imports System.ServiceModel.DomainServices.Hosting
Imports System.ServiceModel.DomainServices.Server

'Implements application logic using the LoginEntities context.
' TODO: Add your application logic to these methods or in additional methods.
' TODO: Wire up authentication (Windows/ASP.NET Forms) and uncomment the following to disable anonymous access
' Also consider adding roles to restrict access as appropriate.
'<RequiresAuthentication> _

<EnableClientAccess()>  _
Public Class LoginService
    Inherits LinqToEntitiesDomainService(Of LoginEntities)
    
    'TODO:
    ' Consider constraining the results of your query method.  If you need additional input you can
    ' add parameters to this method or create additional query methods with different names.
    'To support paging you will need to add ordering to the 'logins' query.

    <Query(IsDefault:=True)> _
    Public Function GetLogins() As IQueryable(Of login)
        Return From login In Me.ObjectContext.logins Order By login.username
    End Function
    
    Public Sub InsertLogin(ByVal login As login)
        If ((login.EntityState = EntityState.Detached)  _
                    = false) Then
            Me.ObjectContext.ObjectStateManager.ChangeObjectState(login, EntityState.Added)
        Else
            Me.ObjectContext.logins.AddObject(login)
        End If
    End Sub
    
    Public Sub UpdateLogin(ByVal currentlogin As login)
        Me.ObjectContext.logins.AttachAsModified(currentlogin, Me.ChangeSet.GetOriginal(currentlogin))
    End Sub
    
    Public Sub DeleteLogin(ByVal login As login)
        If (login.EntityState = EntityState.Detached) Then
            Me.ObjectContext.logins.Attach(login)
        End If
        Me.ObjectContext.logins.DeleteObject(login)
    End Sub

    <Invoke()> _
    Public Function countloginsmatching(ByVal username As String, ByVal password As String) As Integer
        Dim credentials As List(Of login)
        credentials = Me.ObjectContext.logins.Where(Function(t) t.username = username AndAlso t.password = password).ToList()
        Return credentials.Count
    End Function

End Class
once again, a special thanks to techgnome for all the insight.