I have gotten this request a number of times. We used somethign simliar, but this method here works a ton better than the "hack" we used before. VERY Slick.
Link to Microsoft Dynamics CRM Team Blog : Using the attachEvent method to show users context sensitive help
As with anytime you modify the DHTML Code that is NOT documented in the SDK, you should exercise some caution. This example is NOT in the SDK, so be careful and if weird things start happening, remove these BEFORE you call Support. :-)