Dear jinky

Indeed you had to take your time... And you'll find it in the documentation...

In version 4.3.3 (also in other versions) there you can find in the DotNetNuke Skinning.pdf file the different attributes for the solpartmenu. (for instance for the menualignment page 54 = page 58 of the .pdf document).
If you want to center the menu. You've to use menualignement= "center"
You've the possibility to choose {Left|Center|Right|Justify}

But how do you do that?...

You can upload this with your skin (html + xml)
In your .xml file you declare

<Objects>
  <Object>
    <Token>[MENU]</Token>
      <Settings>
        <setting>
          <Name>menualignment</Name>
          <Value>center</Value>
        </setting>
      </Settings>
  </Object>   
</Objects>

Or you can set this directly in your .ascx control
<dnn:MENU runat="server" id="dnnMENU" menualignment= "center" />

If this not helps... then you can perhaps do something like this (HTML-version):
<table>
  <tr>
    <td width="50%">&nbsp;</td>
    <td>[MENU]</td>
    <td width="50%">&nbsp;</td>
  </tr>
</table>

  Hope this will help.