Para abrirlo con el navegador predeterminado yo uso....
en las declaraciones generales:
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
Public Const conSwNormal = 1
en el boton:
ShellExecute Form1.hWnd, "open", "http://www.s2f-proyect.es", vbNullString, vbNullString, conSwNormal