There is a "Fully Loaded/Fully English" ROM created by the fine people at trisoft.de.
You can find this rom at
http://www.trisoft.de/en_c3100howto.htm ==== PLEASE NOTE THAT THIS ROM IS A NAND FLASH IMAGE ====
Let me say that again, for emphasis
==== PLEASE NOTE THAT THIS ROM IS A NAND FLASH IMAGE ====
So please read the documentation on the site. The short form of how to flash this rom is as follows:
1) Unplug AC, remove the battery, the power supply, and any memory cards
2) Hold down the D and M keys on the keyboard and put the battery back in.
(HINT - don't let go until the service menu appears)
3) Slide the battery door switch into the ON (locked) position and plug in the AC adapter
4) Press "UP" twice on the keypad to get to page 3
5) Insert CF card and select "NAND Flash Restore" then press OK
6) Press OK twice to confirm after getting the "NAND Flash Restore from CF"
A green bar will go from left to right, then it will say "Restore OK" .. you can press cancel twice and then remove the AC and battery to reset the Zaurus.