Neither my ftpd nor my httpd are able to deliver files > 2 GB.
So you have to use rsync if you want to fetch the big ISO files from here.

Example:

  mkdir xx
  rsync -avv rsync://ftp.gwdg.de/pub/linux/knoppix/dvd/KNOPPIX_V4.0.2DVD-2005-09-23-DE.iso xx/