You can use a span or a div (and use their onclick events) in the tab and use css to make it behave like an anchor. In fact many other dhtml elements could be used the same way (lots of them have onclick events).

I've just remembered the other way

Stick with your anchors, but at the end of the onclick do a "return false;". I don't know whether that works in all browsers though.

So:

<a href="#" onclick="doBlah(); return false;">click</a>