i'm a big newbie too, and i just got this fixed for me. I have debian sarge, but apparently ubuntu is based off of it.
anyway, go into the filemanager and get to root.
go in etc, this is where configuration stuff is.
I have a folder called "X11", i don't know what you have, but maybe it'll be "xorg" for you. x.org and x86 are the desktop environments, and since you're trying to configure them, that is the place to look
find a file like xorg.config or something. for me it's "XF86Config-4"
now that you know where
it is, it's time to edit it.
unfortunatly you can't edit it as a regular user, so you are going to have to change it as root
open the shell and type 'su' this will change you to root
cd is change directory, so type "cd /etc/X11" or whatever the folder was for you
try kedit XF86Config-4
or whatever the config file you found you wanted
scroll around untill you see some lists of screen resolutions
you might see something like:
Modes "800x600" "640x480"
just change it to be whatever like this:
Modes "1280x1024" "1024x768" "800x600" "640x480"
save it and exit
go to the shell and type exit. this will log you out of the root user, so type exit again.
now, i think i had to restart to get it to work, so try that.
anyway, i don't know if this will work for you seeing as how we have different distros but maybe they're close enough to the same thing.