With webmaster mode, you need to hover over the name of the various .tpl files in the popup window and it will be highlighted with a red border in the the main page. It is probably the best way of locating which file displays what.
In pages.tpl find where it says:
Code:
{include file="dialog.tpl" title=$page_data.title content=$smarty.capture.dialog extra='width="100%"'}
and change it to something like:
Code:
{include file="dialog.tpl" title=$page_data.title content=$smarty.capture.dialog extra='width="100%"' cellpadding="10"}
and in dialog.tpl find this:
Code:
<tr><td class="DialogBorder"><table cellspacing="1" class="DialogBox">
and change it to this:
Code:
<tr><td class="DialogBorder"><table cellspacing="1" cellpadding="{$cellpadding|default:"5"}" class="DialogBox">