(I no longer use the Sharp Zaurus and do not maintain these pages. I have left them here in case they are useful to someone.)
The tkROM is free. It has a very nice look and feel, and the translation to English seems to be complete. I gather the implementation of Linux is a little less cutting-edge than the Cacko ROM. But it seems more stable and (importantly for me) the network applet works.
When you first get your unit, do a NAND backup onto a CF card. That way, you can always revert to how the unit was shipped to you. Instructions are here.
theKompany ROM is here.
You need to download from the website an updater.sh and initrd.bin file for the tkROM. You need to rename the files that you have downloaded to these names.
You will also need a Linux kernel (zImage.bin) from somewhere else, as it is not supplied. You can get it from the Sharp or the Cacko ROM (which I understand are the same). You can get the Cacko ROM package, containing the kernel, here. Extract zImage.bin, and put it with updater.sh and initrd.bin on the root of the CF or SD card that you are using to flash your Zaurus.
Instructions for installation of the Cacko ROM are here. I followed the same procedure for the tkROM. However, the reboot after the installation of the NAND did not work. Once I erased the flash memory it did.
I made a backup of my data using the built-in backup/restore function, using the Cacko ROM. When I tried to restore my data having installed the tkROM, the unit simply rebooted. In other words, I couldn't do it. I am sure this will be obvious to the experts, but it wasn't to me.
The tkROM does not include, by default, a number of the applications you will need. This gives you more choice over what you install (and theKompany makes commercial alternatives to many of the built-in applications, so it makes sense from their point of view). You can download a zip file containing the Sharp applications, including Hancom Word and Sheet, and the PIM apps, [ from the ZUG downloads ].
I got this from the Zaurus User Group here.
If you don't get the buttons, try this:
ln -s /home/QtPalmtop/opera /usr/share/opera
This version seems to me to be less usable than the version in the Cacko ROM, because the navigation icons are so small. But I couldn't get the the IPK in the Cacko ROM download to work.