The only way you can do this is if there are no posts on the wall. If there is nothing on there then it will show the info page as a default to people visiting the group for the first time, i think if they join it takes them to the wall, but every time the group is then visited they will see the info page.
you could always posta message in that part under the profile pic that says write something about this group, and instruct them to visit the info page