Torrents are shared from peer to peer. Newscripts are direct downloads from servers with a number of connections. There is no uploading so their a hell of alot quicker.
I've noticed that alot of torrents are just recycled Newscripts.
Par files are to repair the broken / missing rar files.
Get a subscription to v3 newzbin. Its an indexing site . It costs like $2 a week or month... not sure... You can create NZB's off the site containing some of the PAR files if one of the rar files is corrupt and download in something like news rover. They go through all the NS's and post them up. People also weed out the virus's and NZB's with missing files.
edit: Thats just an example, there are heaps of sites out there that provide these services.