Absolutely positioned, 50% from left and top, with
negative margins of half the div's size. Will push the div
up out of the viewport in IE5/mac (but a CSS filter can fix that).
#middle
Not positioned, uses auto-margins on left and right side
for horizontal centering. That method does not work vertical,
and in IE requires a valid doctype (standards-compliant mode).
For IE5/win we include text-align:center on the parent (in this case #outer).
An empty 50% high div
plus a negative margin of half the height create the vertical centering.
#inner
Text centering methods: Text-align property for horizontal aligning (only
works on inline elements), vertical centering through an
empty 50%-high div
as in the last example, plus a negative margin on the div containing the text:
The number of lines of text in this div times half the line height (0.5 em).
This of course only works if you know the amount of lines, ie. within strictly sized elements.