Hi u are using an Hd5xx try to use the catalyst 9.5 http://wiki.cchtml.com/index.php/Main_Page
Read Me First
Which cards are no longer supported by ATI Catalyst? The ATI Radeon 9500-9800, Xpress200-1250, 690G, 740G, X300-X2500 (including Mobility RadeonHD 2300, since it is really a DirectX 9 part). See the complete list here. If your card is on that list, you are limited to open-source drivers on Debian Squeeze/6.0 (and later). If you really need the proprietary Catalyst/fglrx driver, you will have to use Debian Lenny/5.0.x and install Catalyst 9-3.
ATTENTION RADEON USERS
NOTE: If you enter your card information on AMD/ATI's driver page, it will offer you the Catalyst 9-3 driver to download. However, the Catalyst 9-3 driver doesn't support X servers past 1.5, and it will not work with Debian versions later than Lenny/5.0.x! !!!SO BE CAREFUL!!! If you tried to install Catalyst on a system with one of these cards, see the 'Removing the Driver' section to restore the default/pre-installed drivers.http://wiki.cchtml.com/index.php/Debian
i hope it helps, by the way i dident manageged it either to install the driver proper i have an hd6xx