Hallo!
..., denn border-collapse:collapse lässt alle inneren Ränder verschwinden.
nein, sondern dein margin+padding auf 0
<...>
<style type="text/css">
<!--
table {border-collapse:collapse;}
tr,th,td {margin:0px;padding:10px;border: solid black 1px;}
-->
</style>
und, siehe da:
<table>
<tr>
<th>1</th>
<th>2</th>
<th>3</th>
<th>4</th>
</tr>
</tr>
<td>1:1</td>
<td>1:2</td>
<td>1:3</td>
<td>1:4</td>
</tr>
</tr>
<td>2:1</td>
<td>2:2</td>
<td>2:3</td>
<td>2:4</td>
</tr>
</table>
<...>
mfg Alfie