found 1.04 beta firmware at this site. Haven't tested it yet.
http://www.wiinja.com/belchi.rar
The following are the instructions translated by potatoman ( thanks!!!)
Step 1: install the recovery mode
Put the update.bin file in your card and launch it like other .nds
This will activate the update/recovery mode, which will help you in case of a failure
Step 2: how to install the new firmware
Once installed the recovery mode, you have to rename the bios.bin to update.bin (remember to delete the older one)
Switch on the DS, and press L+R in the original mode while touching the microninja banner (you know, to start the microninja menu, at the time that you can use the pictochat, etc), this will put you into the recovery mode
Then a prompt is shown asking you to update (of course press A)
If there's a problem while updating, you can use the recovery mode