Sorry for needing so much help but:
I tried to install the font size patch again by downloading the RIGHT file,and copying the .jar to /opt/jbpatch, and restarting, but it didn't work.
Also, the developer keys patch doesn't sem to work. I downloaded kindlecalc, copied the azw to documents, and restarting, but I get the message about it not being signed by an authorised develoer.
Edit: I've got the new font size patch now.
Edited edit: all sorted.