This method works on all the new browsers (IE7, Firefox 2, etc) and most old browsers.
.centertbl
{ 
text-align: center;
}
.centertbl table
{ 
margin-left: auto;
margin-right: auto;
text-align: left;
}
			The first style is applied to the <div> that contains 
			the <table>; this will allow MSIE5 and NS4 to center the 
			table. The next style applies to a <table> that is contained 
			within that <div>; the margin settings will allow centering 
			in CSS-compliant browsers and the text alignment will reset the default 
			alignment for table cells to “left” for browsers in which the text alignment 
			of the <div> is inherited.
An example of a <table> styled this was is as follows:
| td1 | Some dummy text here and there. | 
This table was centered by all the browsers tested, and the cell contents also maintained their default left-alignment.