fluxbuntu

On an old machine with few resources, you really should consider fluxbuntu. This “ubuntu”-distro is really fast with the fluxbox windowmanager.
If the X does not fit your needs, you should try Xfce if Gnome (or KDE) runs slowly on your computer. It has a whole lot of nice feature without using up the computer’s resources.

Ubuntu IP6V

Turn off every handling of IP6V in Ubuntu for faster internet.
http://ubuntuforums.org/showthread.php?t=87798
Simply add the file bad_list in /etc/modprobe.d/ with the line:

alias net-pf-10 off

Turn off Firefox 3 urlbar autocompletion

This annoyed me simply too much. It actually made me startup a wordpress blog where I can post my own personal tips - mostly for myself, just to remember!
Everytime I started writing an url, firefox came up with several suggestion based upon history and bookmarks. This got to stop!
Goto: about:config, find browser.urlbar.maxRichResults and set value [...]