I just installed the ATI Radeon HD 6850 from ATi's website and its working fine other than window redraw. When I move a terminal window (or any other window) I get very slow and laggy window redraw. I don't however have a problem with scrolling in non OS related programs like FireFox but I do experience window redraw lag in the file browser when I scroll. I cant figure out what is wrong. I have followed some tutorials on how to fix this problem but none have worked. I have edited my Xorg.conf file and tried to reinstall the drivers but nothing seems to fix this problem. I would like to point out that I am very new to using linux, but I am very willing to learn. I would greatly appropriate any help that anyone could provide.

I have a similar problem with my ATI Radeon HD 6370m.
I think the problem lies with the ATI proprietary drivers ...

You can always just uninstall the ATI drivers to fix the window lag (I don't see any reason to have them, they stop me playing XMoto!), do this by:

cd /usr/share/ati
sh ./fglrx-uninstall.sh

SiberzK