Basically the concept is as such: A DVD is beeing split to multiple pieces of a certain size, in .rar files. Then each .rar file is posted as several mail posts (the usenet program you will use will automatically combine all the posts to one, containing the .rar file). You have to download all the .rar files and then decompress using winrar.
In case you miss any of the .rar files in the sequence, there are .par files posted as well. A par file is a file that can replace ANY .rar you might miss.
Newsgroups are not in the web, there are dedicated news servers (like e-mail or irc servers).
Unfortunatelly, in order to have good newsgroup service to get your job done, you have to pay for a newsgroup server. I would recommend you watch this thread, and if you see something beiing posted that intrests you, then subscribe and get it. You should pay attention on the date of things beeing posted, because when something is posted, it doesen't stay for ever. Good usenet servers keep the file for 10-15 days.
I was reluctant to pay for this service as you might be at first, because I wasn't sure if I would manage to get what I wanted.
I subscribed to a cheap service (www.news.astraweb.com 25GB for $10) thinking that even if i did not manage to get the file I wanted, the loss would not be a great one. I suggest you do the same thing.
Hope this was helpfull.