Hi there
I had same problem - see my post to tips and tricks section - six things I wish I'd known yesterday - there's also a reply to my post there which may help you - I had same problem with 6.1 dvd and ended up archiving other distros, installing knoppix to whole hard drive then reducing reiserfs partition and copying other distros back afterwards - then fixing grub - there must be an easier way - hope one day someone will post it - or fix knoppix hd installer if that's where the problem is???
Best wishes, John