It turns out that the right xorg.conf works (but not the autogenerated from Hardy, and for Gutsy it must be present before the install configures xserver-xorg or it'll hang), provided the NoDDC option is present.  I had that option when I tried in Hardy, but I got the xorg.conf wrong (it really sucks that you have no means of generating xorg.conf for cases where autodetection fails; this has been commented on on other bug reports, but you *really* need to do something about this.  I would consider myself an advanced user but generating an xorg.conf without prompting (like that of dpkg-reconfigure xserver-xorg in gutsy and before) including not autodetecting, but selecting driver and general monitor type (e.g. 1024x768 @ 60Hz)) is quite more than I want to have to deal with.  dpkg-reconfigure doesn't involve learning near as much as writing xorg.conf from scratch).

An I forgot to say that I'm using the alternate installer.

The xorg.conf I used in gutsy (and hardy when the default one failed) comes from http://michaelminn.com/linux/toshiba1800/ and is as follows:

	# xorg.conf (X.Org X Window System server configuration file)
	#
	# Custom file by Michael Minn

	Section "InputDevice"
		Identifier	"Generic Keyboard"
		Driver		"kbd"
		Option		"XkbRules"	"xorg"
		Option		"XkbModel"	"pc105"
		Option		"XkbLayout"	"us"
	EndSection

	Section "InputDevice"
		Identifier	"Configured Mouse"
		Driver		"mouse"
		Option		"CorePointer"
		Option		"Device"	"/dev/input/mice"
		Option		"Protocol"	"ImPS/2"
	EndSection

	Section "Device"
	    Identifier    "Trident Microsystems CyberBlade/i1"
	    Driver        "trident"
	    BusID        "PCI:1:0:0"
	    Option	"NoDDC"
	EndSection

	Section "Monitor"
	    Identifier    "ToshLCD"
	    Option        "DPMS"
	    HorizSync      30-71
	    VertRefresh    50-100
	EndSection

	Section "Screen"
	    Identifier    "Default Screen"
	    Monitor       "ToshLCD"
	    Device        "Trident Microsystems CyberBlade/i1"
	    DefaultDepth    16
	    SubSection "Display"
        	Depth        16
	        Modes        "1024x768"
	    EndSubSection
	    SubSection "Display"
	        Depth        24
        	Modes        "1024x768" 
	    EndSubSection
	    SubSection "Display"
        	Depth        16
	        Modes        "800x600"
	    EndSubSection
	    SubSection "Display"
        	Depth        24
	        Modes        "800x600" 
	    EndSubSection
	EndSection

	Section "ServerLayout"
		Identifier	"Default Layout"
		Screen		"Default Screen"
		InputDevice" "Configured Mouse"
	EndSection


Which I changed to :

# xorg.conf (X.Org X Window System server configuration file)
#
# Custom file by Michael Minn

Section "InputDevice"
	Identifier	"Generic Keyboard"
	Driver		"kbd"
	Option		"XkbRules"	"xorg"
	Option		"XkbModel"	"pc105"
	Option		"XkbLayout"	"us"
EndSection

Section "InputDevice"
	Identifier	"Configured Mouse"
	Driver		"mouse"
	Option		"CorePointer"
	Option		"Device"	"/dev/input/mice"
	Option		"Protocol"	"ImPS/2"
EndSection

Section "Device"
    Identifier    "Trident Microsystems CyberBlade/i1"
    Driver        "trident"
    BusID         "PCI:1:0:0"
    Option        "NoDDC"
EndSection

Section "Monitor"
    Identifier    "ToshLCD"
    Option        "DPMS"
    HorizSync      30-71
    VertRefresh    50-100
EndSection

Section "Screen"
    Identifier    "Default Screen"
    Monitor       "ToshLCD"
    Device        "Trident Microsystems CyberBlade/i1"
    DefaultDepth    24
    SubSection "Display"
       	Depth        16
        Modes        "1024x768" "800x600"
    EndSubSection
    SubSection "Display"
        Depth        24
       	Modes        "1024x768" "800x600"
    EndSubSection
EndSection

Section "ServerLayout"
	Identifier	"Default Layout"
	Screen		"Default Screen"
	InputDevice	"Configured Mouse"
EndSection