It's my understanding that Sharp moved away from the XML format for the Zaurus's PIM applications in favor of a proprietary format as of the v3.10 Sharp ROM version update.

Only pre-3.10 Sharp ROM's (and presumably the various Open Source ROMs) store their PIM data in XML format. The unfortunate thing is that the 3.10 ROM is so far superior to the older Sharp ROM's (IMHO) that it's worth upgrading even if it means having to use the proprietary PIM data format.