As it seems that Linux nowadays is fairly simple operating system for the end user, there is still a lot to learn, it looks like capabilities of the features available for user are unlimited!
After a while the amount of articles, hints and tricks that i have read is simply too much for my poor brains, and it's really not possible to remember everything. I will try to make some notes inhere, so that there will be no need to go through all of the searches once again when i start with a new computer, in the new place, etc.
My computer is not really old, Acer Travelmate 4150 with 1.5 Pentium M CPU and 512 Mb RAM. Ubuntu 6.10 works like a charm on it, but since i work with satellite data, which is fairly large, it will be good to tweak it a little in order to speed the system up.
I've just found a good article on that, written by IBM developers:
Reduce your Linux memory footprint: A few tweaks can boost performance
The best about it that it doesn't say what exactly you have to type in the command line or what to click, but gives a good overview what you should look for, and what is the general idea of how to maximize your computer performance.