Thank you. I note your reservation "....as long as you get the original .torrent file from a reliable source." I don't know what this exactly means."
I prefer virgin copies.
right now, you get that virgin copy off one or another of the centos mirrors, and check its md5 against the master copy on the centos site?
so... get the torrent file from the same place. verify the .torrent control file's md5 before starting the torrent. when the torrent has finished transferring, you can also verify the md5's of the ISO files it contains.
but... the DVD ISO's are on select mirrors, such as http://mirrors.kernel.org/centos/5.6/isos/x86_64/