Earlier versions of Outlook had a group calendar window that was separate from Outlook so you could keep a group schedule visible while working in outlook and other applications. The group calendar was changed in Outlook 2010. Rather than having a separate list of groups that you can display in a scheduler-like window when needed, groups are listed in the navigation pane with all of your calendars. You can collapse the groups to hide the members and check the group to select all, but I feel the old dialog was cleaner.
You have two options:
Right click on a calendar and choose open in new window, then select the group you want to display. You can close the navigation pane on that window and switch to the new schedule view if desired, but its not nearly as good as the old group schedules.
Or select the group in the navigation pane then New meeting, New meeting with all. This will open a new meeting with all of the selected members listed - the scheduler page gives you a view similar to the old group schedules.