at the site below, i have made a step by step tutorial on how to fix your blackberry tour with pics.
the problem with the trackballs is from how the trackball sits on its own little board. in some cases it becomes loose or misaligned, putting a shim in will push the board up to the right height and you will be able to scroll left to right once again.
the direct link to the fix is http://cero.yolasite.com/how-to-open-phones.php
although you don't have to, please click on the ads (you don't have to buy anything / doesnt cost you a thing) so the server i use doesn't think that i am useless to them. think of it as a pat on the back
as always if you have any questions feel free to ask.....