Using your mouse :

·         From the main Internet Explorer menu choose View

·         Then Text Size

• Select your choice of Largest, Larger, Medium, Smaller, Smallest text sizes.

Using the keyboard:

• Open the View menu with the mouse or by pressing Alt+V.
• Select the Text Size option with the mouse or by pressing T.
• Choose your preferred text size with the mouse or by using the up and down arrow keys and pressing Enter or by clicking on it.

Find more information here:

http://www.microsoft.com/enable/training/ie6/fontsize.aspx