had another idea - just found this page
http://zd1211.ath.cx/ which you must have been to before. It says that there are multiple version of the device which means there are different revisions of the same device, so depending on what revision you have your device has a completely different chip inside doing all the work.
So try and find out exactly what revision you device is and what chip is inside it to make sure the zd1211 driver will work for it.
It seems a version of the driver you probably need is inside the 2.6.20 - you knew that right. From looking at the readme in the DEBIAN firmware package from here:
http://packages.qa.debian.org/z/zd1211-firmware.html
You have to ungzip and untar the folder and move the contents of it to /lib/firmware/zd1211 from there the driver should pick it up if the kernel driver is correct and loaded. Try that and then try as root in the terminal:
iwconfig
You should get a list of wireless network interfaces. If you don't the driver might not be loaded in the kernel, so do:
lsmod
and look through the list if it isn't there try as root:
modprobe <driver name>
I'm not sure what the compiled driver is called - do you know?
Chris.