My advice is never to use a text box scrollbar for mobile device sites, as the entire page itself is intended to be easily scrollable it makes little point. If you are trying to keep the advert links or menu buttons in view on screen use CSS to position a div container.
NB: No amount of alternate CSS tweaking is really going to help an existing web site layout become mobile device friendly, they play by different rules on a sceen typically just 320x240 pixels (or 240x320px depending which way you hold it for some)
It's a situation set to get worse again with the release of more mini 'ipad' varients with seven inch screens.. Just as designers thought they would no longer need design for 800x600px screens they make a comeback lol
Here's a ready made mobile template from nokia, works fine on Opera Mini and the HTC browser.
http://www.forum.nokia.com/info/sw....-7470e7ec8576/Nokia_Mobile_Web_Templates.html