Javascript remote rollover - works in IE7 but not IE6

[Ampa]

Working on a new site (http://aboutfaceuk.com/test/ ).

The 'Get In Touch' button (bottom right) is actually a transparent anchor, over a <div> with a background image, containing both the normal and hilighted versions of the contact info.

A very simple piece of javascript changes the background-position to show the hilighted version.

Code: (javascript)

function SecondWaveClass() {
  document.getElementById('SecondWave').style.backgroundPosition="0 -145px";
}

The code works in IE7, Opera, FF but not IE6 and I can't see why?

Any fellow designers / coders have any clues?

Thanks.

[Ampa]

Solved: was nothing to do with the rollover, but rather a limitation of the transparent png hack for IE6 (it can't do position offsets).