Declara esto
Código:
Private Declare Function ShellExecute Lib "shell32.dll" Alias _
"ShellExecuteA" (ByVal hwnd As Long, ByVal lpOperation As String, _
ByVal lpFile As String, ByVal lpParameters As String, _
ByVal lpDirectory As String, ByVal nShowCmd As Long) As Long
Para ver la ayuda
Código:
ShellExecute Me.hwnd, "Open", "C:\ruta_al_html.html", "", "", 1
Con esto se abrirá una ventana del navegador por defecto con el html
Espero que te sirva, un saludo