I think the "a#" you are referring to is the href attribute of a link (<a>). (Tell me if I have that wrong). That is different to the dynamic pseudo-classes, so you can set li:hover and li:active even though there is isn't an <a> or href.
Just tried, the exampel you gave me have an link to hover, active and focus, like this: <td><a href="#"> </a></td> my li to hover or have active is like this: <li>About Us<img src="new_arrow_down.gif" alt="Arrow down" border="0"> <ul>
Just changed the hover to active, to see how it acts on the computer, and on both it is activated on click and as soon as I stop clicking the menu or exemapel disappear.... I Imagine in a touchscreen its just the same, or will it be diferent?