I've dumped the firmware for my A3400IS and it's available here:http://dl.dropbox.com/u/11452962/PRIMARY.BIN
ff88130c Firmware Version 1.01
ff881328 Firmware Ver GM1.01A
ffc32f47 JN B
ffc3316c Copyright (C) 1997-2011 by CANON Inc.
ffc331f0 DRYOS version 2.3, release #0050
Note that I could not get the firmware version displayed using the Set+Disp buttons. I've tried multiple times with ver.req and vers.req, but nothing worked and the display didn't show. I'm wondering whether this may also impact getting access to the CHDK menu.
Instead, there was a file on the sd-card in the MISC directory with these contents: