[carpeperdiem]

in file /skin1/customer/main/products.tpl
FIND:

{if $usertype eq "C" and $config.Appearance.products_per_row ne "" and $config.Appearance.products_per_row gt 0 and $config.Appearance.products_per_row lt 4 and ($featured eq "Y" or $config.Appearance.featured_only_multicolumn eq "N")}

REPLACE WITH:

{if $usertype eq "C" and $cat eq "1" or $cat eq "2" or $cat eq "3" }
{include file="customer/main/products_t2.tpl" products=$products}
{elseif $usertype eq "C" and $config.Appearance.products_per_row ne "" and $config.Appearance.products_per_row gt 0 and $config.Appearance.products_per_row lt 4 and ($featured eq "Y" or $config.Appearance.featured_only_multicolumn eq "N")}

edit the $cat eq "1", etc.. to your cat numbers
CLONE your products_t.tpl and make it look how you want it -- I called mine, products_t2.tpl

This code basically looks for category 1, 2 or 3, and instead of using the normal products_t.tpl, it uses products_t2.tpl

OR -- just buy Jon's mod and it will be MUCH simpler - AND you can then have an assortment of templates to use at any time, for any category. You only change the source once ( for the mod) and that's that.