In home.tpl, remove the two instances of this line of code to get rid of the margins:
Code:
<TD width="6"></TD>
The space between categories and bestsellers is due to a
between the two. Look for this code in home.tpl and remove the break:
Code:
{ include file="customer/categories.tpl" }
{if $active_modules.Bestsellers ne "" and $config.Modules.bestsellers_menu eq "Y"}
{ include file="modules/Bestsellers/menu_bestsellers.tpl" }
{/if}