no problem, figured there wasn't much dutch in it anyway
here goes:
You no doubt have the experiabox of KPN, more people are having the same problem. I found the solution after some puzzling moments.
A short explanation:
1) go to http://192.168.2.254
2) Username: KPN is filled in already, Password is blank, or you changed it before, then log in using your password.
3) Go to Network at the top of the page
4) Go to WLAN at the left of the page
5) Use these settings:
Enable WLAN: Yes
Mode: IEEE 802.11g Only
Channel: 7
Transmitting power: 100%
Enable WMM QoS: No
WiFi should work properly now
You are the best, thanks a lot!