sysinstall 6.1 b1 input/output error "unable to transfer" from both CD or FTP

[David Armour]

hello list
in the middle of installing freebsd [6.1 b1] over an earlier 
ubuntu trial during transfer from CD to hard drive, i began to 
see "unable to transfer ... from acd0" error messages for first 
the doc, manpages, dict, and base distributions. i switched the 
install media to ftp and successfully installed the doc, manpages 
and dict distributions (i think!) before again encountering the 
"write failure on transfer" error for the  base distribution.

i burned the install cds at a 16x speed and 'verified' them with 
nero, if that makes any difference.

my archive searches with the errors above pasted in produced 
conflicting or dated results. is there a way to easily narrow 
down the list of culprits? any help greatly appreciated.