I was making things too compicated. The first if statement was working so I just cut out the whole second if statement with an {else}. This is how it worked in case, for some off the wall reason, someone else wants to do this:
{if $main eq "catalog" and $current_category.category eq "" OR $smarty.get.pageid eq "24"}
{include file="customer/main/welcome.tpl" f_products=$f_products}
{else}
<div id="middlecolumn">
I really need to spend some time learing smarty and php better. Can anyone recommend a good place to start? I live in Bulgaria, so books in english are hard to find and cost more to ship than to purchase.