your specs are nothing specifically interesting, all you'll get is a popularity contest, which you can get any time you want at http://distrowatch.org
. just try one and if you like it, stick with it. only concession you'll need to make is the desktop environment, which is not distribution specific. KDE3 (or 4) or Gnome 2 may well be too much, but any distro running that will struggle on a 900mhz compared to a 3ghz one, regardless of which one it is.