With border-collapse set to collapse, the solution would be to use an inset border for all the cells, and a solid border for the cell that the mouse hovers over. Here's the suggested CSS in action: http://jsfiddle.net/QmHGG/

The following is the CSS that was applied to the table:

table, tr, td {
    border: 1px inset black;
    border-collapse: collapse;
    border-spacing: 0;
}

td:hover {
    border: 1px solid red;
}

<style type="text/css">
    table {
        border-collapse: collapse;
    }
    #one td {
        border: 1px solid #ff0000; 
    }
</style>

<table>
    <tr id="one">
        <td></td>
        <td></td>
    </tr>
    <tr id="two">
        <td></td>
        <td></td>
    </tr>
</table>