The usual "centering" used for form labels and inputs is actually 2 columns, labels right-aligned and input-fields left-aligned.
One way to do this without tables is to give the label elements the same width and right-align them, for example:
<style type="text/css">
.foolabel{width:10em;text-align:right;display:inline-block;margin-right:1em;}
.formlist{list-style:none}
</style>
<ul class="formlist">
<li><label class="foolabel">Name:</label><input type="text" /></li>
<li><label class="foolabel">Quest:</label><input type="text" /></li>
<li><label class="foolabel">Favorite Color:</label><input type="text" /></li>
</ul>