I then also still a bit of research and found that there is this WLAN stick Longshine which is excellently supported by Mac OS X 10.6. Install drivers, stick with the MacBook connect, enter the DNS address of the router and WPA2 key. Finished!
The performance is perfect. One point deduction is available for the bulky casing. In order to use adjacent ports (Mini DisplayPort and additional USB port), you have to use a USB extension. An approximately 15 cm long cable is included.