I was able to install beta4 by following the below instructions:
First installation - new bootloader
1) Good idea make NAND backup before
2) Format CF or SD card (MMC unworking for me) with FAT16
3) Extract bootloader and emergency files to card. There must be updater.pro, u-boot.bin, emergenc.img
4) Extract rootfs and kernel files to this or another CF or SD card, there must be: rootfs.img kernel.img autoboot.sh
5) Run diagnostic menu (D+M) and run NAND Flash Erase from Extra Menu.
6) Turn OFF your zaurus. Unplug power adapter, eject battery.
7) Insert SD or CF card with extarcted files (if you insert both CF and SD, updating fails)

Press and hold "C" and "D" keys and plug power adapter (battery must be ejected!).
9) Green LED must light on for ~20 sec.
10) If both LEDs flashing, that mean bad CF or SD, or non FAT16.
11) When Green LED off, unplug power adaptor.
Bootup emergency system
1) Insert SD or CF card with pdaXrom
2) Press and hold OK button and plug power cable
3) Wait for 10 sec and leave OK button
4) Screen on and emergency system will booting
5) After booting, it will detect SD or CF card and run autoboot.sh script
7) After flashing, it will reboot and pdaXrom will booting - time for battery insert:)
The system runs fine now but if I turn off my Zaurus I cannot get it to turn back on. I have reboot it (by removing the battery and power)