You will need:
A backup of your Psion's disks (this is very important as everything in your C: drive will be lost; your D: drive should escape, but don't count on it.
The Psion installer;
Arlo for your model of Psion (5 or 5mx);
A glued kernel image;
A compressed initrd;
A paperclip or similar, thin, blunt item (to reboot your machine).