'Tipos, constantes y funciones para FileExist
Const MAX_PATH = 260
Const INVALID_HANDLE_VALUE = -1

Private Type FILETIME
        dwLowDateTime       As Long
        dwHighDateTime      As Long
End Type

Private Type WIN32_FIND_DATA
        dwFileAttributes    As Long
        ftCreationTime      As FILETIME
        ftLastAccessTime    As FILETIME
        ftLastWriteTime     As FILETIME
        nFileSizeHigh       As Long
        nFileSizeLow        As Long
        dwReserved0         As Long
        dwReserved1         As Long
        cFileName           As String * MAX_PATH
        cAlternate          As String * 14
End Type

Private Declare Function FindFirstFile Lib "kernel32" Alias "FindFirstFileA" _
    (ByVal lpFileName As String, lpFindFileData As WIN32_FIND_DATA) As Long
Private Declare Function FindClose Lib "kernel32" _
    (ByVal hFindFile As Long) As Long



Public Function FileExist(ByVal sFile As String) As Boolean
    'comprobar si existe este fichero
    Dim WFD As WIN32_FIND_DATA
    Dim hFindFile As Long

    hFindFile = FindFirstFile(sFile, WFD)
    'Si no se ha encontrado
    If hFindFile = INVALID_HANDLE_VALUE Then
        FileExist = False
    Else
        FileExist = True
        'Cerrar el handle de FindFirst
        hFindFile = FindClose(hFindFile)
    End If

End Function


'Para usarla:
If FileExist("lo que quieras comprobar") Then
   'El archivo existe
Else
   'El archivo no existe
End If