Is it possible to boot from the install CD and then access the hard drive? If so, how do I do it?

find out the what the partition you want to mount is..

fdisk -l

(say the partition is /dev/hda1)
do this as root:

mount /dev/hda1 /mnt

cd /mnt

to access your stuff..

See the section on this wiki page about using the CD as a rescue disk: http://www.knoppmythwiki.org/index.php?page=BlackScreenAfterInstall

There are actually a number of pages on the wiki with directions for doing one thing or another like this, copying original version of lost or damaged files from the CD, using the CD to fix your lilo config and reinstall it, ...