I strongly suggest that you stay away from that site, or any other mirror.

See the links near the top of this page? Click on the Documentation link to go to the wiki, then read the Download FAQ. It will explain what file/(files) you need, the merits of using BitTorrent over the problem prone mirrors, and several other things that are very important to know about properly burning the disc.

If you want a CD you'll have to stick with 5.1.1, if you want a DVD then 5.3.1 is newer (but it's menus are much more sloppy and garbled, much of the good stuff is harder to find. I'm not sure that there is much merit of 5.3.1 over 5.1.1 even for DVD users).

After reading the Downloading FAQ you should know how to get the files, but right next to the Documentation link above is a Get Knoppix link. That should get you started.

Was there a reason why you text was all in bold? It really doesn't get you a better or faster response, and some people may be inclined to not respond at all when posts are done in such a manner.