It appears that you have built a new "define page" named mypage, and made a set of nested tables to output your content. You don't have any useful class or id tags on the elements, so it will be tricky to get a border as is; however, if you add appropriate tags, the border becomes trivially easy. Your current output:
HTML Code:
<table width="100%" border="0" cellspacing="2" cellpadding="2">
<tr>
<td class="breadCrumb"> </td>
</tr>
<tr>
<td class="pageHeading" align="center"> <h1>This is mypages heading!</h1> </td>
</tr>
<tr>
<td class="main">
<table width="400" border="0" cellspacing="2" cellpadding="2">
<tr>
<td align='center'><a href='index.php?main_page=tshirt&act=showdesign&did=34&view=design'><img src='designs/small/3drinks-150.gif.gif' border='0' width='175' height='175'></a></td> </tr>
</table>
<div align="center" class="tabletxt">
</div>
</td>
</tr>
<tr>
<td class="main"> <a href="http://totallycooltees.com/store/index.php?main_page=index"><img src="includes/templates/template_default/buttons/english/button_back.gif" alt="IMAGE_BUTTON_BACK" title=" IMAGE_BUTTON_BACK " width="39" height="15" /></a> </td>
</tr>
</table>
The "breadcrumb" part does not belong in this section at all (notice the real breadcrumbs just above the <td> you tagged breadcrumb.)
It would be much simpler and more flexible if you scrap the old-fashioned tables and just use a few divs which you can style in your stylesheet:
HTML Code:
<div id="mypageContent">
<h1 class="pageHeading"> This is mypages heading!</h1>
<div class="imageLink"><a href='index.php?main_page=tshirt&act=showdesign&did=34&view=design'><img src='designs/small/3drinks-150.gif.gif' border='0' width='175' height='175'></a></div>
<div class="text"> </div>
<div class="backButton"> <a href="http://totallycooltees.com/store/index.php?main_page=index"><img src="includes/templates/template_default/buttons/english/button_back.gif" alt="IMAGE_BUTTON_BACK" title=" IMAGE_BUTTON_BACK " width="39" height="15" /></a> </div>
</div><!--mypage content-->
The border becomes
#mypageContent .imageLink img {border: 3px inset #aabbcc;}
Adjust to taste.