A Japanese programmer has posted a Playstation 1 emulator for the Zaurus. You can download the file from here. Click on "ZAUUP". The file is called "PCSX for X/Qt". I have not tested this. In fact, I've never run X on my Zaurus, but I would be interested in hearing if others are able to get this to work and how fast it is. There doesn't appear to be much documentation.
P.S. I'm just the messenger, and not the programmer.