Start the libretto in DOS mode, or in DOS, if loaded connect your pcmcia cdrom or network card or scsi with hd and type ladlin vmlinuz initrd=initrd51.gz
If you are lucky it will work. Have fun ;-) It worked for me with a Panasonic KXL-740.
This information was obtained from the website of Victorgv, victorgv@bu.edu http://www.geocities.com/SiliconValley/Haven/5112/. Do NOT try to download initrd51.gz from this page, it hangs, use ftp above.
This worked for me with the Libretto 50CT from DOS, with no problems!