Handle the ItemAdd event for the Items collection for whatever public folder
you want, then call the Win32 API sound routines to play the sound.

Here's what the Win32 API calls would look like:

Public Declare Function sndPlaySound Lib "WINMM.DLL" Alias _
 "sndPlaySoundA" (ByVal lpszSoundName As String, ByVal uFlags As _
 Long) As Long

Public Const SND_SYNC = &H0
Public Const SND_ASYNC = &H1
Public Const SND_NODEFAULT = &H2
Public Const SND_LOOP = &H8
Public Const SND_NOSTOP = &H10

Public Sub PlaySound(SoundName As String) 'must be .WAV file
 Dim wFlags As Integer
 Dim X As Integer

 On Error Resume Next

 If SoundName <> "" Then
   wFlags = SND_ASYNC Or SND_NODEFAULT
   X = sndPlaySound(SoundName, wFlags)
 End If
End Sub