I wrote a script to do that for you. [1] (and am having my server download the first fifty listed in the xml file).
I'd like to point out that there's a little bit under a thousand talks, so I highly recommend you only download a few videos at a time. (each video is about 40 mebibytes. [2] Roughly 40 gigs of video.)
then we can script to extract the xml file get the ted videos, like:
wget -c -O "1984/Nicholas Negroponte in 1984 makes 5 predictions.mp4" http://www.ted.com/talks/download/video/4837/talk/230 wget -c -O "1990/Frank Gehry as a young rebel.mp4" http://www.ted.com/talks/download/video/4047/talk/231 wget -c -O "1998/Aimee Mullins on running.mp4" http://www.ted.com/talks/download/video/5996/talk/443
...
wget -c -O "2011/Wadah Khanfar - A historic moment in the Arab world.mp4" http://www.ted.com/talks/download/video/11071/talk/1084 wget -c -O "2011/Wael Ghonim - Inside the Egyptian revolution.mp4" http://www.ted.com/talks/download/video/11086/talk/1086