Ok, did a quick test and this seems to work:
Download compat-wireless-2.6.tar.bz2 from http://wireless.kernel.org/en/users/Download
and cw.fixed.chan.patch from: http://forum.aircrack-ng.org/index.php?topic=8373.0
Place them in the same folder and navigate to it.
I didn't run the install step, but all the rest ran without errors. If you get error during the make process, you probably just need to install some dev packages.
tar -xvf compat-wireless-2.6.tar.bz2
patch -Np1 -i ../cw.fixed.chan.patch
sudo make install
A new iwlagn.ko will be in ./compat-wireless-2011-02-28/drivers/net/wireless/iwlwifi/iwlagn.ko after compilation, but you should run the make install step to make sure it gets installed correctly.