TED videos can be downloaded directly from their website:
You can also get it through their RSS feed if you want.
The videos on TED can be downloaded directly from the website. But if you want to download videos from TED in batch, use a streaming video downloader will be more effcient. I use Video download capture to do this job. You can have a try, I think this program won’t let you down.
ted2mkv downloads TED videos and all their subtitles and creates a standalone (with subtitles embedded) mkv file.
you could also look into this : http://obinshah.wordpress.com/2012/07/01/ted-v3-0-the-tedinator/
it downloads subtitles too alongwith different video quality