Welcome to X-Cart! Please be sure to post your full version in your signature (i.e. 4.0.1
. Each version is different, and this information is very important.
You can use the orderby function to solve your issue. Use an {if} statement like this to only show categories with an orderby under 500:
{if $categories[cat_num].order_by < 500}
This would go in customer/categories.tpl