For Internet Explorer: look down RHS bottom of your window... you can change the size of stuff in the window there.
For Outlook: You can make the text or font in the pane larger or smaller by using the scroll wheel on your mouse. Using the scroll wheel is the only way you can change the text size, although more options are being considered for a future version of Outlook.
Click in the Reading Pane, press CTRL, and roll the scroll wheel. Rolling the wheel away from you makes the text bigger, rolling it towards you makes the text smaller.