If someone could please help out here and show me what exactly I'm doing wrong.

First of all, I am using an ATI Radeon HD 5770, just now uninstalled and installed the latest driver as well as OpenCL.
Next, registered at btcguild.com, created a "worker" there.
Downloaded the latest version of the GUIminer.
Run guiminer.exe.

Now I am unable to chose the GPU instead of the CPU and have a terrible mhash/s ratio.
Do I have to change some settings in the Catalyst Control Center to get OpenCL to work and thus enable the GPU as an other choice?


Edit: Nevermind, finally got it working.