On tables with a large number of rows, scrolling down forces the column headers off of the screen, and you can lose track of what you're seeing.  This bit of CSS will allow you to scroll just the body of the table and leave the headers in place.  It works quite well in Firefox, looks good in Internet Explorer if your table doesn't have a "caption" tag, and degrades to standard table display in other browsers.

People in My Group
Name Relationship
me of course!
George imaginary friend
Daryl my brother
Daryl my other brother
Co 1a co-worker
Co 2a co-worker
Co 3a co-worker
Co 4a co-worker
Co 5a co-worker
Co 6a co-worker
Co 7a co-worker
Co 8a co-worker
Co 9a co-worker

The table above was produced like this: 

 
<style type="text/css">
    .ScrollTable-container {
      display:table-cell;
    }
    .ScrollTable thead tr {
      position: relative;
    }
    .ScrollTable tbody {
      overflow: auto;
    }
    .ScrollTable tbody tr {
      height: auto;
    }
    .ScrollTable tbody tr td:last-child {
      padding-right: 20px;
    }</style>

-------------------------------------------------------

<div class="ScrollTable-container">
  <div class="ScrollTable" style="height: 200px;">
    <table> 
      <thead>
        <tr><th colspan="2">Heading</th></tr>
        <tr><th>Column 1</th><th>Column 2</th></tr>
      </thead>
      <tbody style="height: 135px;">
        <tr>
          <td align="left">Label1</td>
          <td align="left">Data1</td>
        </tr>
        <tr>
          <td align="left">Label2</td>
          <td align="left">Data2</td>
        </tr>
      </tbody>
    </table>
  </div>
</div>