Horizontal tearing

I was wondering what exactly causes horizontal tearing - ever since I started using my 9800 pro, Half-Life is chopped apart by it. Are there any settings I can change to fix this?

This is how I understand it: Tearing occurs because your card is displaying too many frames per second. It's drawing a future frame when it's only half way done drawing the current one. This happens because your monitor refresh rate is far lower than the actual fps coming from your 9800.

First thing to do is turn on vsync in the ATi control panel. This will draw the frames as fast as your monitor refreshes (85 Hz -> 85 fps). I still get some tearing in older games like quake 3 and half-life with my 9800 and vsync on, but it's much better.

There are about 15 tabs in the contol panel which one controls the VSYNC toggle?