I have installed kubuntu and ran programs such as knoppix and DSL on the computer. All of these OS's have not taken up the entire screen. I haven't done anything to the resolution settings and it still only takes up part of the screen.
My computer is a Dell laptop, 14 in. screen, Inspiron 1100, Celeron 2.4Ghz processor, 256 MB ram, and 30 GB of memory.
I just had windows xp on this computer and it took up the whole screen and I never had a resolution problem.
Everything regarding graphics and resolution is either (depending on your linux distro) in /etc/X11/XF86Config-4 or /etc/X11/xorg.conf.
Those are the files that you will need to access at the command line.
You will want to see what your monitor is read as.
It is probably not being read correctly.
I have a Viewsonic PF790 monitor that is rarely read correctly and I have to edit my /etc/X11/xorg.conf file to correct this.
Yep, in the command line, either:
as root. To get root:
and type your password (that won't appear as you type, normal).
Google around to find the right settings.