[JWait]

What you are referring to is the "title". The problem is, it shows up on all pages, not just in your categories.

Open skin1/customer/main/subcategories.tpl for editing and find ..
{include file="dialog.tpl" title=$current_category.category content=$smarty.capture.dialog extra='width="100%"'}

Change it to...
{include file="dialog.tpl" content=$smarty.capture.dialog extra='width="100%"'}

Save and upload.

This should make it not display the title. If the title still shows up then the next easiest way to achieve what you want is to make a copy of skin1/dialog.tpl named dialog-blank.tpl (I use "-" instead of "_" so I will know I made it and it is not a x-cart default file). Then, in dialog-blank.tpl find where it says...

<tr>
<td class="DialogTitle">{$title}</td>
</tr>

and comment it out so it looks like this...
{* <tr>
<td class="DialogTitle">{$title}</td>
</tr> *}

Save it, then upload to skin1/dialog-blank.tpl.

Re-open skin1/customer/main/subcategories.tpl for editing and find where you edited...
{include file="dialog.tpl" title=$current_category.category content=$smarty.capture.dialog extra='width="100%"'}

Change it to...
{include file="dialog-blank.tpl" content=$smarty.capture.dialog extra='width="100%"'}

Save and upload.