the category products list you should modify the "<xcart_dir>/skin1/customer/main/subcategories.tpl".
1) add the following code:
{if $subcat.categoryid ne 249 and $subcat.categoryid ne 250}
right after these strings:
<table cellspacing="0" cellpadding="5" width="100%"> {foreach from=$subcategories item=subcat}
where 249 and 250 are the category IDs which you need to hide.
If you want to hide only one category (i.e. Logos, its ID is 249) you should add this string:
{if $subcat.categoryid ne 249}
instaed of
{if $subcat.categoryid ne 249 and $subcat.categoryid ne 250}
2) add the following string:
{/if}
just before these strings:
{/foreach}
</table>
{/if}
If you have problems applying the modification, I can do it for you for you