Found here: http://www.mithis.com/zaurus/ipkgs/
Install opie-sh_0.5-20030824_arm.ipk (needed for the graphical interface), then oz-compat_0.5_arm.ipk, then oz-compat-opie_0.1_arm.ipk.
Tried it. Downloaded them, unpacked the tar files, put them on CF, and used the package installer under the settings tab. opie_sh... appears to install ok, or at least without obvious errors. The other two packages get "Invalid magic" in the package installer. I also tried used ipkg directly from the console, with the same result.
A few side notes: I was not able to install the Opie/OpenEmbedded ROM while Cacko was intalled. I had to go back to the original Sharp ROM (via a NAND backup) and then install Opie.
If mains power is plugged in when Opie suspends itself after enough inactive time, it doesn't come back on again when the "on" button on the spine iof the c860 is pressed. I had to unplug mains power before it would respond.
Perhaps its just a matter of being older than the Opie developers, and perhaps there is a package that will help, but many of the default fonts are hopelessly too small to be readable.
A few times, Opie completely blanked the screen for a second or two, and then came back, for no obvious reason. The screen also seemed to blink sometimes when it reduced the blacklight after enough inactive time.
Sigh. Back to Cacko for the moment. Don't have enough time this week to install the development kit and try to fix any of these problems, although a few of them (fonts?) should be easy.