Grazie Alex del preziosissimo aiuto, alla fine son riuscito a risolvere così:
Private Sub limg_DblClick(Cancel As Integer)
Dim F As Object
Dim strFile As String
Dim strFolder As String
Dim varItem As Variant
Dim P, h, com, num As String
com = Forms![1scalb]![Comune].Value
num = Forms![1scalb]![N° Albero].Value
Set F = Application.FileDialog(3)
F.AllowMultiSelect = False
F.InitialFileName = "D:\Test DB\media\" & com & "\" & "0" & num & "*"
If F.Show Then
For Each varItem In F.SelectedItems
strFile = Dir(varItem)
strFolder = Left(varItem, Len(varItem) - Len(strFile))
P = strFolder & strFile
Next
Else: GoTo ERR
End If
Set F = Nothing
'MsgBox P
h = Mid$(P, InStrRev(P, "media"), InStrRev(P, "\"))
Me.limg.Value = h & "#" & P & "#"
ERR:
Me.limg.Undo
Exit Sub
End Sub