Detecting Systemwide User Idle Time in Windows XP with Visual Basic .NET

Hello all,
          This might be a silly question but I just can't figure it out and any help would be greatly appreciated.

I am trying to code a routine in Visual Basic .NET that will tell me how long the user has been idle (how long since no keyboard and mouse input has been detected.) If idle time exceeds a certain ammount of minutes, my program needs to pop up a message and do other things.

I have tried to use the API GetLastInputInfo in order retrieve this information, but it is just not working.  Here is the code I am using:

In a module, I have added:

'-----
    Public Structure LastInputInfo
        Public cbSize As Long
        Public dwTime As Long
    End Structure

    Declare Function GetLastInputInfo Lib "User32" (ByRef lastinfo As LastInputInfo) As Boolean
'-----

And my form code reads something like this (I have ommited Windows Form Designer Generated Code for the sake of clarity):

'----
Private Sub Timer1_Elapsed(ByVal sender As System.Object, ByVal e As System.Timers.ElapsedEventArgs) Handles Timer1.Elapsed

        'Timer is set to run every second

        Dim res As Boolean
        Dim info As LastInputInfo

        info.cbSize = Len(info)
        res = GetLastInputInfo(info)
        MessageBox.Show(res & " " & info.dwTime.ToString)
          ' This messagebox is there for debug purposes.  It ends up showing that res is False and
          '  info.dwTime.ToString is 0; indicating the function has failed.

          ' I have also omitted the code to test for elapsed idle time, etc, since the point here is to
          '   show the function is failing.

End Sub
'----

What I don't understand is why the function is failing.  I must be doing something wrong, either when declaring it, or when calling it.

I don't necessarily have to use GetLastInputInfo, I just thought using that API would be the easiest and 'cleanest' way of telling how long the system has been idle.  I am open for other solutions as well.  Just keep in mind my program is coded in Visual Basic .NET and I know nothing of C++.

Any help greatly appreciated. Thank you very much!