After reading reports 15700 and 12276, I did an strace as suggested there and
here's the result:

ubuntu@ubuntu:~$ strace -p $(pidof esd)
Process 17651 attached - interrupt to quit
select(6, [4 5], NULL, NULL, NULL
 <unfinished ...>
 
and after nothing more had happened for three by-the-watch minutes, I did a
ctl-c and got 
 
Process 17651 detached

Should I have let it run longer?  A return to ^-alt-F7 still had the blank
screen, and nothing had changed on ctl-alt-F3 or F4 either.  By the way, I was
wrong earlier in saying I couldn't get to a command prompt from the brown
screen.  I just hadn't pressed the function key quite long enough.  Sorry; my
mistake.

I also did a

gdb /usr/bin/esd $(pidof esd)

and got back  

attaching to program: /usr/bin/esd, process 17598

(this being a different time & so different pid for esd), and then a string of
alternating messages:

reading symbols from [...] (no debugging symbols found) ...
loaded symbols for [..same as above...]

(i.e., where [...] were different, but the "reading" and "loaded" lines
alternated, and the "reading line" always had "no debugging symbols found" in
it.  And when I did, while in gdb, a "bt," it returned the following:

#0 0x0fe3b504 in select () from /lib/libc.so.6
#1 0x100050ec in clean_exit ()
#2 0x10003aa8 in clean_exit ()
#3 0x0fd8c80c in __libc_init_first () from /lib/libc.so.6
#4 0x0fd8c80c in __libc_init_first () from /lib/libc.so.6
#5 0x0fd8c80c in __libc_init_first () from /lib/libc.so.6
previous frame inner to this frame (corrupt stack?)

As for the terminal screens, ctl-alt-F1 didn't show much interesting: just the
same lines as appear in brown under the "reflected" logo: 

 * Setting the system clock...                  [ ok ]
 * Synchronizing clock to ntp.ubuntulinux.org...
Error : Temporary failure in name resolution
                                                [fail]
 * Initializing random number generator...      [ ok ]
 * Setting up X server socket directory...      [ ok ]
 * Setting up ICE socket directory...           [ ok ]
Last login: Sun Feb 14 00:26:44 1984 on tty2
Linux ubuntu 2.6.12-9-powerpc #1 Tue Oct 4 10:53:08 EST 2005 ppc GNU/Linux

and after that of course the free/no warranty blurb and a command line.    

Ctl-alt-F4 is shown next, below.  Does it indicate a problem with the CD I
burned?  (I checked the md5 sums on the download, but can't recall whether I had
the burning s/w verify the CD.  Usually I do, but I can't swear I did this
time.)  But given how far the installer got, and given what I saw next on
ctl-alt-F4, I'm more inclined to suspect a locales issue.

Anyway, ctl-alt-F4 shows:

Feb 14 05:21:31 casper: Mounting snapshot...
Feb 14 05:21:31 kernel: [  246.064610] cramfs: wrong magic
Feb 14 05:21:31 kernel: [  246.079234] Unable to identify CD-ROM format.
Feb 14 05:21:31 kernel: [  246.085545] EXT2-fs warning: maximal mount count
reached, running e2fsck is recommended
Feb 14 05:21:32 casper: Scanning for swap devices...
Feb 14 05:21:32 casper: Found /dev/hda4
Feb 14 05:21:32 casper: Using swap devices: /dev/hda4
Feb 14 05:21:55 root: register-modules
 * Entering runlevel: 2
 * Starting system log daemon...                        [ ok ]
 * Starting kernel log daemon...                        [ ok ]
 * Starting system message bus...                       [ ok ]
 * Starting Hardware abstraction layer:                 [ ok ]
Starting pbuttonsd: pbuttonsd 0.7.1: iBook/G3 PB Pismo/G4 PB Titanium (PMU
version: 12)
 * Starting GNOME Display Manager...                    [ ok ]
 * Starting Common Unix Printing System: cupsd          [ ok ]
 * Starting HP Linux Printing and Imaging System        [ ok ]
 * Starting PCMCIA services...                          [fail]
 * Starting powernowd...
 *  CPU frequency scaling not supported
                                                        [ ok ]
 * Starting Bluetooth services...
 hcid sdpd                                              [ ok ]
 * Starting deferred execution scheduler...             [ ok ]
 * Starting periodic command scheduler...               [ ok ]
Last login: Sun Feb 14 00:26:44 1984 on tty3

& then the same ID/date of Linux, free and no warranty blurb, and a command
prompt.  I am copying it for you above just for completeness, and just in case
the cramfs "wrong magic" and "unable to identify CD-ROM format" messages are
relevant.  But what looks to untutored, merely guessing me like a more likely
problem is the following, from ctl-alt-F3:

insmod /lib/modules/2.6.12-9-powerpc/kernel/drivers/ide/pci/generic.ko
insmod /lib/modules/2.6.12-9-powerpc/kernel/drivers/ide/pci/cmd64x.ko
insmod /lib/modules/2.6.12-9-powerpc/kernel/drivers/ide/pci/aec62xx.ko
insmod /lib/modules/2.6.12-9-powerpc/kernel/fs/nls/nls_base.ko
insmod /lib/modules/2.6.12-9-powerpc/kernel/fs/isofs/isofs.ko
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
        LANGUAGE = (unset),
	LC_ALL = (unset),
	LANG = "C.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
locale 'fr_Fr.UTF-8' valid and available
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
        LANGUAGE = (unset),
	LC_ALL = (unset),
	LANG = "C.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
locale 'en_US.UTF-8' valid and available
Reading package lists...
Building dependency tree...
console-tools is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
[  545.609436] Linux Kenel Card Services
[  545.613428]   options:  [pci] [cardbus] [pm]

and then the last login time for tty1, Linux ubuntu ID and time, and free and no
warranty lines before the login.

The warning about the locale setting having failed seems odd, but it could
explain why no desktop is shown: which desktop should it display in what
language?  I saw that first when I chose English & US, so I tried again with
French, and then with Czech (those being the only other two languages whose
keyboards and words I know), with essentially the same results.  If it were an
install to the HD, I could edit etc/default/init; but of course the live CD
isn't writable.

What do you suggest as a workaround?  First stop xorg & gdm, and then just do a
setenv and then start a new session?  Hmmm, as I ask that, I get a sinking
feeling I did only half of what I should have done over the weekend: I didn't
try a locale command, nor a setenv LANG or setenv LOCALE command, either.  I'll
try those next, but won't delay this message to do so.

Fwiw, I also noticed that if I chose Czech, for example, as the language at the
outset, I would receive the progress messages in the blue and red %-bar screens
in that language -- e.g., nastava se sit pro DHCP, etc., *until* the "preparing
for live system" message -- which appeared in English, at 26% for "configuring
language" (in English); there was one more message in the chosen language
(setting up the keyboard -- nastavuje se klavesnice), but then it was all
English again.  I don't know that that's necessarily related to the failure to
set locale and language, but maybe it's relevant.  

HTH.