connecting Airport Express to Belgacom Aethra FS4104 AW rout

I am trying to connect an Apple Airport Express to my Aethra fs4104-aw.
What does one have to do to connect Airport Express to the Aethra router which is configured to using PPPoE.
I have the idea that there is a IP conflict since the Airport hangs whenever I try to configure it to connect to the Aethra.
All setttings are standard incl Wireless.
I have put the Aethra also in bridge mode without luck.
Thank you
What does one have to do to connect Airport Express to the Aethra router which is configured to using PPPoE.
I have the idea that there is a IP conflict since the Airport hangs whenever I try to configure it to connect to the Aethra.
All setttings are standard incl Wireless.
I have put the Aethra also in bridge mode without luck.
Thank you