HTML/CSS: what's a better option for layout of a tree of nested elements than nested tables?

<ul>
    <li><input type="checkbox" />Vehicles <ul>
        <li><input type="checkbox" />Unpowered</li>
        <li><input type="checkbox" />Bicycle</li>
        <li><input type="checkbox" />Skateboard</li>
    </ul></li>
    <li><input type="checkbox" />Powered <ul>
        <li><input type="checkbox" />Two-wheeled <ul>
            <li><input type="checkbox" />Motorcycle</li>
            <li><input type="checkbox" />Scooter</li>
        </ul></li>
        <li><input type="checkbox" />Four-wheeled</li>
     </ul></li>
</ul>

Edit: a little css & js to show & hide nested elements (no checkboxes)

li.opened ul {
display: block;
}

li.closed ul {
    display: none;
}

and js...

$(document).ready(function() {

$('li input:checkbox').click(function () {
    $(this).parent().toggleClass('opened');
    $(this).parent().toggleClass('closed');
});

$('li').addClass('closed');
});

edit, again, because Sparr wants some better styles (assuming that the checkboxes have a style of "checkbox"

li input.checkbox { /* input:checkbox is not 100% compatible */
    width: 6px;
    margin: 0 2px;
    /* This makes 10px be the total "width" ofh the checkbox */
}

ul {
    margin: 0 0 0 10px; /* Or whatever your total checkbox width is */
    padding: 0;
}

li {
    padding: 0;
}

You could do this:

<ul>
  <li>
    <input type="checkbox" /> Option 1
    <ul>
      <li><input type="checkbox" /> Option 1 Sub Option A</li>
    </ul>
  </li>
</ul>

You'd then set the padding/margin of the UL's to 0 and 0. Then set the padding-left of the LI's to 10px.

ul {
  margin:0;
  padding:0;
}

li {
  margin:0;
  padding:0 0 0 20px; /* Each nested li will be padded incrementally */
}

For the javascript, attach an event to each checkbox that determines whether the sibling UL (if any exists) should be visible. If the box is checked, show it, else, hide it.

Nested unordered lists are best practice for this sort of thing.

<ul>
   <li>Item 1</li>
   <li>Item 2
      <ul>
         <li>Sub Item 1</li>
         <li>Sub Item 2</li>
         <li>Sub Item 3</li>
      </ul>
   </li>
   <li>Item 3</li>
   <li>Item 4
      <ul>
         <li>Sub Item 1</li>
         <li>Sub Item 2</li>
         <li>Sub Item 3</li>
      </ul>
   </li>
</ul>