If you can get your hands on a USB CD drive, that might be worth a try. I used one to install DSL on a notebook a few years newer than yours. Sadly only to give up thanks to lack of drivers afterwards.
Sadly, the Libretto L5 has exceptionally picky USB boot support, only works with a very small selection of drives that were mostly not sold in the USA. So not really an option.
I actually have all the drivers for it from an old fanforum for the series ^.^'...