Try the standard Sharp ROM, with the localization and translations installed. There are many documents on how to do this around the internet. I'm sure someone can point you to one.
Unfortunatly the Addressbook and e-mail will NOT correctly (for English speakers) alphabetize the listings. You might be able to get a different Zaurus version running on this, like one from the 6000 or something to correctly alphabetize these things, if you really need that.
Now, I'm just going on what I know from reading 860 user posts, because, as it says in my signature, I have a 5600.