How to export files from hard drive in Snow Leopard CD?
Keep in mind that you are booted to a different volume/system when you boot to the installer DVD.

With that in mind you can use ls /Volumes to get a list of volume names.

Presumably you will see Macintosh HD (or different name if you renamed the internal volume) listed, if so you can use cd /Volumes/Macintosh\ HD to switch to the internal drive. If your internal drive is named differently then keep in mind that spaces should be replaced with \ (a backslash followed by a space) in Terminal. Once you're in the correct volume your earlier commands should work as expected.

That same ls /Volumes command should show the path of your external hard drive as well.  You could copy the files using something along the lines of cp /Volumes/Macintosh\ HD/file1.jpg /Volumes/Backup\ Drive/Folder1.

If you are attempting to copy everything from the hard drive you can use the following command to force a copy of everything, skipping over corrupted data that would otherwise cause the process to hang or stop...

cp -Rfv /original/data /destination/drive


or, following my previous example

cp -Rfv /Volumes/Macintosh\ HD/ /Volumes/Backup\ Drive/