Boot Linux from a FireWire device (developerWorks)
Once you have booted with the install CD, with a bit of luck it should have recognized your drive. The drive should appear as a disk under /dev/sdX, where X is a lowercase letter starting at "a." On my system, the external drive was detected as /dev/sda, but this will vary if you have other SCSI disks (or emulated SCSI disks); in that case, it might be /dev/sdb or some other letter. If your drive is not detected automatically, some further steps may be required -- for instance, you might have to pass boot options to enable FireWire or PCMCIA, or you might have to manually load some kernel modules, or other things of that sort."