Well, the answer depends on how you define your pages. If you are using a table-based html layout, you need to use the <center> </center> tags, and place them either side of the main table definitions. i.e. like this:
HTML Code:
<center>
<table>
TABLE CONTENTS
</table>
</center>
I dunno quite how you would do this in a pure CSS layout, but I imagine the same tactic would work if you put centering around the DIVs (provided, of course, that you haven't set absolute positions for any of the graphics.
The dropshadow is rather harder i'm afraid. You'd be best to make it a graphical dropshadow, as CSS ones tend to have variable browser compatability.