changing package installation path
 

i use the unitedlinux distribution, i installed it as normal using the CDROM
so the installation source is /medis/cdrom.
now i have the source in a folder (hard disk), the command apt-get reads the
list of installation sources before run, how can i add the folder path to te
list file?( i tried to edit it but it didn't work)
by the way i tried to change the yast2 installation path but it reported an
error when i choosed a local folder (hard disk), why?
thanks so much