Changing the characteristics of the default font in Word is very easy to do. Here’s how:  
In Word 2003, go to the Format menu and select Font to open the Font dialog box.

In Word 2007 or 2010, click on the Font dialog launcher in the Font group on the Home tab. That’s the little diagonal arrow down at the bottom right hand corner of the Font group.

Once you have the Font dialog box open, customize the font as you want your default font to appear. You may select the font style of your choice, as well as the font size and any other characteristics such as color, bold, underline, etc.

When you’re all done, then click the Default or Set as Default button down at the bottom of the Font dialog and then respond with Yes when Word asks if you are sure.

A similar technique will work with PowerPoint as well, although you will have to work a little harder in order to specify font selections for text headings, sub-headings, and text body.