A few tweaks can boost performance can boos Linux desktop performance.
The ideas in this article may help you breathe life (and some additional security) into your old machines and make better use of Linux on aging hardware.
A lack of physical memory can severely hamper Linux performance. In this article, learn how to accurately measure the amount of memory your Linux system uses. You also get practical advice on reducing your memory requirements using an Ubuntu system as an example.
This article will help you select appropriate Desktop environment, Browser, Office application, IM client etc.
Read rest of all optimization tips : Reduce your Linux memory footprint [ibm.com]