<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
About your xhtml parceing question. The DTD should be global and all browsers should treat it the same. Too bad enternet explorer doesn't support anything. I don't even think it supports html.
Off hand I would say that there is no easy way out of this proublem. I personally have never delt that much with the margin css attribute mostly due to my protest of xhtml and the W3.
It is proublay just a IE proublem. Personally, how I would do it....
[html]
<div style="width:100%;">
<div style="width:750px;">
All of the body content goes here.
</div>
</div>
[/html]
text-aling, only aligns text in FF. You cant center a page useing it.