Similar to the old real-estate adage 'location, lOcation, location', getting more RAM, RAM, RAM will provide a great improvement. All processes need memory, and whenever the kernel runs out of RAM, it starts swapping to disk, but as this is orders of magnitude slower, your performance takes a hit. If you are willing to spend something, don't hesitate. Go out and get some extra RAM sticks for your machine. As soon as you plug them in, you will notice better performance. Getting more RAM isn't very costly, and it doesn't require any configuration or re-installation.
Even if you don't want to spend the money for more RAM, you can make Linux manage the available RAM in a more efficient way. Here are some simple .changes to consider:

•Change from KDE or GNOME to a lighter desktop environment. GNOME is about the worst in terms of RAM requirements (although it's far below that of Windows Vista), and KDE is a close second. Try using a less-demanding environment, such as
Xfce or Enlightenment. Other possibilities include IceWM, Blackbox, Fluxbox, Fvwm, JWM or (the now seemingly defunct) Window Maker. Note that these window managers are not exactly" equivalent to having a full desktop environment, so you will have to adapt a bit. Plenty of popular distributions, such as DSL (Damn Small Linux) or Puppy Linux use these lightweight window managers, and many are available as optional packages for Red Hat or SUSE.



•Get rid of fonts you never use. I was once a fonts junkie and loaded my box with several hundred fonts (I'm not exaggerating) just in case I might use them some day. Each font requires memory, and the fewer fonts you have, the more RAM you will free. And, some programs will run faster, because they will have shorter lists of fonts to load.

•Reduce the number of virtual desktops. Windows users work with only one desktop, but do you really need 16 virtual desktops in Linux? Experiment a bit with this. I wouldn't go down to one desktop, but most of the time, having two or three virtual desktops is more than enough.