I have already installed Linux on 3 laptops, and not surprisingly I had the same problem on two of those. I am talking about a Toshiba Pro 4600, a Toshiba Pro A10 and a Clevo M761S. The A10 was the only unit where installation had no display problems. It is suspected that vesa compatibility driver is the common factor. A10 has an nvidia (no problems), 4600 a Trident and the M761S the much feared sis 771/671 chipset.
How did I solved the low-resolution problem on the Clevo and the reduced 4600 display? Simple, editing:

# sudo cp /etc/X11/xorg.conf /etc/X11/xorg.old

above line just saves your old file in case you want to get back to your previous settings.

# sudo mousepad /etc/X11/xorg.conf

You are free to replace "mousepad" by the editor of your choice, gedit, vi, you name it...
Locate the section "Monitor". It will look like this:

Section "Monitor"
 Identifier "Configured Monitor"
EndSection

Make it look like this:

Section "Monitor"
 Identifier "Configured Monitor"
 HorizSync 28-72
 VertRefresh 43-60
EndSection

Save and reboot
If something goes wrong, login at the bash (text-mode) prompt and enter:

# sudo cp /etc/X11/xorg.old /etc/X11/xorg.conf

and reboot again, you will be back to the old settings.
To know exactly what is your new resolution range and where you stand, issue the command:

# xrandr -q
Its output will give you something like this:

Screen 0: minimum 640 x 480, current 1280 x 768, maximum 1280 x 768
default connected 1280x768+0+0 0mm x 0mm
1280x768 0.0*
1024x768 61.0
800x600 61.0
640x480 60.0

Note the little * on the second line, that is where you are.
If we want to change the resolution, just type:

# xrandr -s 1280x768

And the display will change instantly...

For those needing an Ubuntu Intrepid 8.10 SIS 771/671 2d display driver, you may find it here, courtesy of Mr. Barros Lee.
Save it, open a terminal on the directory where you saved it, log in as root with the su command and execute

./sis_vga_drv_161208-Ubuntu810.run

edit /etc/X11/xorg.conf, adding Driver "sis" in Section "Device"

For Jaunty 9.04 32-bit click here.
For Jaunty 9.04 64-bit click here.

For Karmic 9.10 32-bit click here to get the driver I compiled.
For Karmic 9.10 64-bit click here to get the driver I compiled.

For Lucid 10.04 32-bit click here to get the driver I compiled.
For Lucid 10.04 64-bit click here to get a driver I compiled with the precious help of Jonas Schwabe.

In these 4 later cases, you should add Driver "sis671" in Section "Device".
On 9.10 and 10.04, not having a default xorg.conf, click here to download a xorg.conf that can be copied to /etc/X11 (don't forget it has to be done in su mode).