If they used the split command, then appropriate way to put it all back together is to use cat.
cat first.iso second.iso third.iso fourth.iso fifth.iso sixth.iso seventh.iso eighth.iso > KNOPPIX_V4.0-2005-06-08-LINUXTAG2005-DVD-DE.iso
Code:
james@dualcrush:~/spl# ls
DD.mp3
james@dualcrush:~/spl# split DD.mp3
james@dualcrush:~/spl# ls
DD.mp3  xab  xad  xaf  xah  xaj  xal  xan  xap
xaa     xac  xae  xag  xai  xak  xam  xao  xaq
james@dualcrush:~/spl# cat xa? > DD-combined.mp3
james@dualcrush:~/spl# ls
DD-combined.mp3  xaa  xac  xae  xag  xai  xak  xam  xao  xaq
DD.mp3           xab  xad  xaf  xah  xaj  xal  xan  xap
james@dualcrush:~/spl# md5sum DD*
9b44e9be0c8df1363aaee4e825eb06ad  DD-combined.mp3
9b44e9be0c8df1363aaee4e825eb06ad  DD.mp3
james@dualcrush:~/spl#