Lighter Window Manager. If you're using the default Gnome or KDE which come with RH9, they will in themselves be using a fair chunk of your valuable system resources. There are plenty of others you can try which will make better use of your available RAM - I don't know what comes with RH9, never having used it, but XFCE or IceWM might be good choices. Others might suggest Fluxbox or Blackbox, but they might be something of a culture shock after Gnome/KDE....
I use XFCE on occasion, and it's noticably snappier than KDE, even with 512mb of RAM.