As long as you fix the width of the table itself and set the table-layout property, this is pretty simple :
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<style type="text/css">
td { width: 30px; overflow: hidden; }
table { width : 90px; table-layout: fixed; }
</style>
</head>
<body>
<table border="2">
<tr>
<td>word</td>
<td>two words</td>
<td>onereallylongword</td>
</tr>
</table>
</body>
</html>
I’ve tested this in IE6 and 7 and it seems to work fine.