ATI Catalyst drivers slowness

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http://askubuntu.com – I have managed to install the drivers, but after installing those drivers moving different windows such as browser is very laggy. Why is that? I also tried older drivers, but they all have the same problem. I have ATI Radeon HD5850. I installed this driver: AMD Catalyst™ 11.11 Proprietary Linux x86 Display Driver. I can't remember how I installed it, because I installed Ubuntu again because of the drivers. All I remember that it was very easy. The file was .run. I have only one screen (Asus VE247**) (HowTos)