Cannot connect pda to wifi enabled lan

Hello,

I cant seem to figure out the problem. I have a wireless network setup in my home, using a wifi enabled DSL router (D-Link). I have been able to successfully connect to the internet through wifi using my notebook and my PS3, but I have never had any success connecting any of my PDA's (neither under WM 5.0 nor 6.0). My PDA's detect the wifi access point, but when attempting to access it, the WEP code is never accepted (and if I turn off all authorization, it simply gets stuck at "Connecting" and never actually connects).

Does anyone have any idea what might be the problem, because I am completely clueless at this point. What exactly is going on?