The most important thing is - How much RAM have you got? Is Windows XP struggling because you are low on RAM? Part of your trouble is that you want Firefox and OpenOffice. They are both heavy on using RAM. If you Google "Linux Dell Latitude C800" you will see quite a lot - Debian, Fedora, Suse ...and Ubuntu. You might be better to stay away from the Gnome and KDE desktops (minimum 256Mb RAM) and aim at something like the Xfce desktop (minimum 128Mb RAM)