adding OnClick method to a href link

[Jeff]

Hi

..NET 3.5

In my webpage I have a link which I want to perform some logic when clicked.
I want it to perform only that logic and not go to another webpage. Because
the code behind the OnClick event will change the display mode of a div on
my webpage (making that div visible)

So I started with this:
<a onclick="OnClick()">Helloworld</a>
But here "Helloworld" is just plain text, which nothing happens when
clicked.

any suggestions?