The DHT is a distributed way of getting your .torrent files and connecting to them without a tracker (as classic BitTorrent uses). Tribler, if you use the built-in search function, uses the DHT for both.
What root is suggesting is not to throw away your Windows installation. Ubuntu images, since they are free and well available, are great for testing whether you can actually download using a BitTorrent client. What we'd like you to do is to download the .torrent file provided by that link and then try and download the Ubuntu image by adding the .torrent file to Tribler. That way you can test whether Tribler can actually download - without depending on the DHT. It's step 1 to try and figure out your problems.
If you feel like trying Ubuntu afterwards, be my guest - though I'd suggest Wubi
at first. If you don't that's quite fine as well.