Configuring Fritz!Box to use WEP (For Nintendo DS)

Hey Guys

I've got a Nintendo DS Lite and I was wandering if I could play online with it. I tried connecting to my router but Nintendo DS's only support WEP. And since my router uses WPA-PSK, I can't use it as an acces point. Can somebody help me to configure my router so it will use WEP acces ONLY for the Nintendo DS and still keep using the WPA-PSK connection for my computer. My router is a Fritz!box 7170 with firmware version 58.04.82. I use Sitecom Wireless Utility 2.1.6.0 as my networking utility.

Thanks in advance.