Hi, I just got the ipw2100 to work on my dell 600m laptop. I can't tell why it's not working for you so here is exactly what i did.
I downloaded the firmware from sourceforge using firmware version 1.3.
Unzipped and moved to:
then "modprobe ipw2100".
then I shutdown with shutdown -h 0.
Restarted , iwconfig , and it worked.