Using a DLL in VB

I am new to using DLLs in Vb and am having a problem accessing a DLL function.  I have a DLL with the following IDL file:

//**********************************
// Generated .IDL file (by the OLE/COM Object Viewer)
//
// typelib filename: prxySayHi.DLL
[  uuid(1D5A64A8-6705-4156-B4B6-0354E3A96A3F),  version(1.0)]
library prxySayHi
{
    // TLib :     // TLib : OLE Automation : {00020430-0000-0000-C000-000000000046}
    importlib("stdole2.tlb");
    // Forward declare all types defined in this typelib
    dispinterface _intfcSayHi;
    [
      uuid(2D02AD08-4CB8-4857-8CAB-85828BFC8CFD),
      helpstring("Generated on Tuesday, March 20, 2007 03:43:39 PM")
    ]
    dispinterface _intfcSayHi {
        properties:
        methods:
            [id(0x00000001)]
            long methdSayHi(
                            [in, out,
                custom({F0D491D0-0DF9-4ECA-AFB0-5C573ABE9325}, "100")            
           
] BSTR* vDataBuf,
                            [out,
                custom({F0D491D0-0DF9-4ECA-AFB0-5C573ABE9325}, "0")            
           
] long* tpurcode);
    };
    [
      uuid(2E2E8AFE-DEBD-4C51-952C-105C89C98627),
      appobject
    ]
    coclass intfcSayHi {
        [default] dispinterface _intfcSayHi;
    };
};
//**********************************
The purpose of the DLL is just to pass a "Hello" message back to the calling program.

I am using VB 2005 Express to write the calling program.  I have creaded a button to execute the call and a text field to display the "Hello" response.
When I view the dll in the object browser, I see two options available: prxySayHi.intfcSayHi and prxySayHi._intfcSayHi both showing my methdSayHi with appropriate variables.

If i call it using  prxySayHi.intfcSayHi I get the following error:
'Unable to cast COM object of type 'prxySayHi.intfcSayHiClass' to interface type 'prxySayHi._intfcSayHi'. This operation failed because the QueryInterface call on the COM component for the interface with IID  "
This is the code I'm using:
'**********************-Start-***************************
Public Class GetHi
    Private Sub cmdGetHello_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdGetHello.Click
        Dim intRetVal As Integer
        Dim strDataBuf As String
        Dim intUrCode As Int32
        Dim objCSayHi As prxySayHi.intfcSayHi
        objCSayHi = New prxySayHi.intfcSayHi
        strDataBuf = "Hi"
        intRetVal = objCSayHi.methdSayHi(strDataBuf, intUrCode)
        Me.txtHelloMsg.Text = strDataBuf
    End Sub
End Class
'**********************-End-***************************

If I try to use the interface type 'prxySayHi._intfcSayHi' usning the following code I get other errors.

'**********************-Start-***************************
Public Class GetHi
    Private Sub cmdGetHello_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdGetHello.Click
        Dim intRetVal As Integer
        Dim strDataBuf As String
        Dim intUrCode As Int32
        Dim objISayHi As prxySayHi._intfcSayHi
        objISayHi = New prxySayHi._intfcSayHi
        strDataBuf = "Hi"
        intRetVal = objISayHi.methdSayHi(strDataBuf, intUrCode)
        Me.txtHelloMsg.Text = strDataBuf
    End Sub
End Class
'**********************-End-***************************
With this code on the 'objISayHi = New prxySayHi._intfcSayHi" line I get an error : "'New' cannot be used on an interface.      "
If I remove this line I get the following warning: "Variable 'objISayHi' is used before it has been assigned a value. A null reference exception could result at runtime."
If I ignore the warning and run the app I get - amazingly - a "NullReferenceException was unhandled" error.

I know I must be donig something stupid but I'm missing it.  Any suggestions???

Thanks,  Diane

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