The standard Ubuntu release is a little bloated, primarily because it runs the full Gnome desktop environment. There's a version called Kubuntu which uses KDE, which is also heavy on the system. If you already use Ubuntu elsewhere, I would recommend trying
Xubuntu, which uses a more lightweight "window manager" called Xfce, and lighter Office apps rather than the full OpenOffice.
Note that installing one Ubuntu version doesn't lock you in e.g. if you installed the standard version, and you have some disk space, you can add the "xubuntu-desktop" meta-package over the Internet. You then choose which one "window manager" to launch at the login screen (select "xfce" or "GNOME" from the Session menu). I'm getting more in to Xubuntu on my netbook - which is not very powerful, though I still use OpenOffice on it.