Outlook 2010 displays Date Navigator as part of To-Do bar and by default it displays one month. But there is a option available for the Outlook users to change the number of months displayed in Date Navigator.
Click the View menu and navigate to Layout section and click the down arrow available below the To-Do Bar section.
Select Options from the drop down list.
This would display the To-Do Bar options as shown below
If you want the Date Navigator to display 2 months then enter the value for Number of month rows as 2 and click the Ok button. Now the Date Navigator would start displaying 2 months.