No doubt there are many of you that already know this, as it is so basic, but I just learned about this a week or so ago, and I wanted to pass it along. Mostly because the default font on this forum is so small!
If you have Windows (I don't know about Vista), and you want to change the size of the print you are reading, hold down the Ctrl key and move the scroll wheel on your mouse, if you have one. If you don't, quit reading. Personally, I couldn't have another mouse without a scroll wheel.
That's all!