Wolfgang, the fn-key problem that you describe here also appeared when I went from 64-bit Karmic to Lucid on my HP ProBook 4510s, which has an ATI Mobility Radeon HD-4330. The fn-key problem disappeared after I installed ATI Catalyst Display Driver version 10.6, which I downloaded from the AMD support site.
Wolfgang, the fn-key problem that you describe here also appeared when I went from 64-bit Karmic to Lucid on my HP ProBook 4510s, which has an ATI Mobility Radeon HD-4330. The fn-key problem disappeared after I installed ATI Catalyst Display Driver version 10.6, which I downloaded from the AMD support site.