The easiest way would be to use the install cd1 to boot the system as if you were going to install.
After you get to the login then from the cli (command line);
~#mkdir /slacktemp #temporary mount point
~#mount /dev/your_device /slacktemp #this is the device you installed to
~#chroot /slacktemp #change to yours
You should now be able to do edits or whatever to your system.