One of the new features in Office 2013 is Hardware Graphics Acceleration which is supposed to improve performance. It doesn't always work well on older computers (and even some new ones). Symptoms include blurred text, cursor hangs randomly, and Outlook freezing for a few seconds (or longer).
Two proven ways to resolve this problem are:
1. Use a non-Aero theme for Windows. Do this by right-clicking on your desktop and selecting Personalize from the context Window. Select one of the non-Aero themes.
2. You can disable the use of Hardware Graphics Acceleration (for the entire Office 2013 suite) from the Options dialog of any Office 2013 application. Each application that is open will need to be closed and restarted after changing the setting.
In Outlook 2013, go to File, Options, Advanced and select Disable Hardware Graphics Acceleration, near the bottom of the dialog.