The firmware (01.06 as of this blog post) has been made available for some time now at padbbs
It has also been mirrored here. The files must be moved to the internal SD card root directory (md5 and img files).
Connect the device to the computer via USB.
Make sure you mount the device as a USB storage device for it to be visible to your computer. You do not need to install drivers on a typical Windows PC to perform this operation.
Then you need to turn the device off.
While holding the menu AND home butons, turn on the device. This puts you into recovery mode.
First choose to ‘update ramdisk’. Then ‘update system’.
It is recommended that you choose ‘wipe data/factory reset’ as well, but you will lose your settings and data on the device. This is not always necessary.
When this is all done, choose to ‘reboot system now’.
Reboot the device:
Android Market on 12.18 firmware: