vertical centering with CSS2

I have been unable to figure out how to "vertically center" things using
CSS2. To illustrate what I mean, consider the following:
 
<div style="width:300">
            <div style="width:20%; margin-left:auto;
margin-right:auto">text</div>
</div>
 
That centers the inner div horizontally, but what if I want to center it
vertically? The spec states that for absolutely positioned block level
elements, "margin + padding + height = container height", but it makes no
such requirements on normal, statically positioned blocks. Is there a
different way to do this?
 
Thanks for any help you can give me,
Nolan Clark