I booted from CD in /dev/hdc, then unpacked some tarballs into / (mostly into /usr/local, also into /extra, so I don't think I clobbered anything used by the system).
I'd stuff in a flash drive and finnix recognized it (I was it added /dev/sda1 in /proc/partitions), and I was able to mount it fine.
The problem began when I did a 'df -k', I started getting repetitive messages about a problem with /dev/hdc. (Sorry, the machine is in another location so can't be more specific). When I tried to do a shutdown, it hung.