newsgroups have been around a long long long time
originally started as a text based message posting system divided by group hierarchies, it wasn't long before someone figured out by using standard ASCII code you could encode jpg's into ASCII and then have then decoded one the post was retrieved with 3rd party software, that eventually lead to MIME encode / decoding and then it evolved as they figured out how to post mp3s, movies etc..
now with advent of par files ( to ensure a post extracts even if all the files are not present ), yenc encoding ( to make the posts smaller ) and automatic extracting software ( Grabit ver 1.7 beta ) grabbing what not from Usenet ( newsgroups ) is easier than ever.
there are private newsgroups servers ( like Giganews Supernews, or my favorite Shemes.com ) which sell download by the gigabytes for monthly or one time useage fees and there is your own ISP new-servers.
some ISP such as SBC and AT&T have dropped newsgroups alltogether.
the subject is far to complex for me to explain,
you best off going to shemes.com and download grabit
and google newsgroups faq to see what newsgroups is and how to "susbscribe" to it