Comment 8 for bug 276990

Try compiling this iwlagn module, http://www.orbit-lab.org/kernel/compat-wireless-2.6/2008/10/compat-wireless-2008-10-01.tar.bz2 .
Extract the archive to your home directory then follow these steps

sudo apt-get install build-essential
cd compat*
make
sudo make install

Then restart your computer. It worked perfectly for me, if it works for more people perhaps the default ubuntu module will be upgraded.

PS> I was not able to test on 802.11g since I only use n and b.