To install Psi-OS v2.7b onto your Siena, extract this ZIP file and, using PsiWin copy the directories that are produced from this ZIP file onto your Psion. Now install Psi-OS onto the system screen by using the key combination of PSION-I. Now install the Setup program in the same way you did Psi-OS.

Run Psi-OS. And it should set up its files on your Psion. Psi-OS allows some files to be deleted if you are trying to cut down on space (see below),

LOGO.SYS
START.DAT

Once installed and run for the first time, Psi-OS is set up ad ready to go!