EDIT: #1: The iwlwifi wifi drivers for both 4965 and 3945 are now in the mainstream kernel, as of 2.6.23, which is now available in Sid. Just install it, and you shouldn't need to do anything else thats described here.
#2: I finally decided to update the top part of this, using information thats from all of the subsequent posts. Although, I would still recommend you read all of the other posts, because I haven't been fiddling with this driver for a couple months, and other people are more knowledgable about this than me.
This howto is to try and get Intel 4965 wifi cards, found in the Santa Rosa chipset, working. Since the iwlwifi driver is not yet in the Debian repositories, to get it to work requires you to download that and compile it yourself. There are a couple of deviations from the normal "Make" "Make install" process to get it to work properly, so here they are.
This Howto assumes a 2.6.22 kernel, which has mac80211 already built in. I assume if you compile and load it for 2.6.21, it should work, but I haven't tested that.
1. Make sure you have linux-headers-2.6.22-1 and linux-source-2.6.22 downloaded from the Debian repositories.
2. Unpacked the linux-source-2.6.22 into the /usr/src folder. This is the same folder that the .tar file is downloaded to.
3. Go here and download the newest 4965-ucode package(or just do an "apt-get install firmware-iwlwifi, with non-free enabled), and the newest iwlwifi package.
4. Then do a "tar xvf" for the ucode package, and then move it into /lib/firmware.
5. Then do a "tar xvf" for the iwlwifi driver. It doesn't matter what directory you do this in, I did it in my /home folder.
6. Then do a "ln -s /usr/src/linux-source-2.6.22 /lib/modules/2.6.22-1-amd64/source"
7. Then cd to your iwlwifi folder, "make" and "make install". That should be all thats necessary.
Any corrections much appreciated, for content as well as style. I've never written a howto before. Also, there are still errors in this driver; for example, on my T61, it requires network manager to be installed and I have to do an "ifdown wlan0" and "ifup wlan0" after I log in. (I've actually gotten it to work with nm-applet now, so I don't have to do this anymore)