You should use the XHTML Strict DOCTYPE, you might try that. If not it's better to write XHTML anyways.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"
http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
If it doesn't work, then you can use text-align: center;
Like this:
HTML:
<div class="outerContainer">
<div class="innerContainer">
<p>Your Stuff</p>
</div>
</div>
CSS:
div.outerContainer { width: 980px; margin: 0 auto; text-align: center; } /* This will center the outerContainer in IE6, obviously set the width to whatever you want */
div.outerContainer div.innerContainer { text-align: left; }
You can use two divs for this because that way the 2nd div (innerContainer) will reset the text-align property to 'left'. You can also put floats etc on the innerContainer. That's how I usually do it anyways.
But for IE7, I know that when using the XHTML Strict DOCTYPE, you don't need text-align: center, the margin: 0 auto will work. Sometimes it works in IE6 too... lol but I've seen IE6 not work for whatever reason. Infact I've seen it do unbelievable things. IE6 is a ridiculous browser by today's standards.
Anyways, that should help.