Only tried this once but this is how I got 1280x800 working on my laptop.
(Acer Aspire 3680 - KInfoCenter in the PCI section reports graphics controller as:
Intel Corporation Mobile 945GM/GMS/940GML Express Integrated Graphics Controller (rev 03))

Boot knoppix livecd with:

knoppix lang=us noswap screen=1280x800

(of course only the "screen=1280x800" is important here)

once fully booted, and have a working internet connection
open console and enter following sequence of commands:

su
apt-get update
apt-get install 915resolution

(915resolution is the key, and runs automatically on install)

close console,
chose Logout from the applications menu,
chose "End Current Session" from the Logout menu,
Current session closes, new session starts in 1280x800 resolution.

Hope this might help someone who is having the same trouble as I did getting 1280x800 to work.