Well, if you really want it all centered (I'm warning you, though, it looks terrible) find this in your quote_randomquote template:
HTML Code:
<tr><td class="alt1" width="30%"></td>
<td class="alt1"><div style="font-style:italic;margin-right:10%;">
<p>"$randomquote[quote]"</p>
<p style="font-weight:bold;margin-left:25%;">- $randomquote[author]<if condition="$randomquote[context]"> ($randomquote[context])</if>
and replace it with this:
HTML Code:
<tr>
<td class="alt1" colspan="2"><div style="font-style:italic;text-align:center;">
<p>"$randomquote[quote]"</p>
<p style="font-weight:bold;">- $randomquote[author]<if condition="$randomquote[context]"> ($randomquote[context])</if>
That should solve it, but I haven't had time to test it.