Boy, this is an odd one. I think I ran into it myself, though.
There are a couple of things you need to do, I think. When you set the ip address, I think you may need to add an up statement to the command:
ifconfig ndis0 inet 192.168.1.50 netmask 255.255.255.0 ssid default wepmode on wepkey 0x(key) up
Does your console say anything when you run the command? It should perk up and display something when you run the command to initialize the device. Additionally, you might want to email the freebsd-portables mailing list for suggestions-- they seem to be the major forum of discussion for Project Evil. Additionally, you could ask Bill Paul, the author of NDISulator. If you go this route, you need to do a few things:
Give a copy of your dmesg output with the card installed. Give the exact syntax command you use to load the module, and to intialize the card (eg, kldload, then ifconfig). Also, indicate exactly which version of driver you're using-- downloaded from the website, from the driver CD. If possible, attach a copy of the driver you're using. Also, indicate the exact model of the card, and which chipset it is that the card uses. Most importantly-- don't do your work in X-- do all of it at the command line, so you can get the messages that are provided.
If you provide even the most minute of details, you will get a great amount of help. Just don't waste his time by giving the "gist" of anything-- tell him exactly what the steps you took were,exactly what your hardware is, and how you're using it.