Checkbox when checked, disables textbox.

I'm looking for the easiest way to do this:

I have a text box and a check box.  

When some one checks the check box, I want the text box to immediately disable and have its text = "";

Alternatively, when the box is unchecked, I want the text box enabled again.

How can I do this without having to jump through a bunch of hoops?

Essentially, I want the checkbox changed event to runat="client" but that does not work.

Thanks.